Arknights Guide: Best Operators To Promote For RIIC Base Skills

Last Update: 12/11/21 - updates for updated Bubble Skill

Arknights does a great job of teaching us that each Operator has a Skill that applies a buff to a Facility in the RIIC Base when the Operator is assigned to work in that facility.  What is NOT explained well is that Operators gain additional RIIC Base Skills at higher Promotion Levels. The other thing that is not obvious is what those Skills are.  In this guide we will recommend Operators that are worth considering for Promotion for the second RIIC Skills that they gain.

First, it should be noted that the Promotion Level at which the Operator gains their second RIIC Skill depends on their rarity.  The extra Skill is typically gained as follows:

• 1 and 2 Star: Upon reaching Level 30

• 3 and 4 Star: Upon reaching Elite 1

• 5 and 6 Star: Upon reaching Elite 2

Note: This is not a guide to the best buffs for each facility.  This guide only looks at the buffs gained from Promotion.  If you are interested in finding the best buffs for each facility, a full list of the RIIC Base Skills can be found on the page linked after this paragraph.  The list can be filtered on Facility, Promotion Level, and Server (NA/CN).  It can also be sorted by buff size to easily find the Operators with the best buffs, or be grouped by facility.

Note: This guide will refer to different RIIC Base builds, such as 2-5-2.  If that doesn’t mean anything to you, then refer to our RIIC Base Guide first before reading this guide:

Formula credits: ScifiGemini0616#3863

This guide does not attempt to provide specific "time to pay off" Promotion estimates because it is extremely variable, and can change depending on factors such as:

• the size of the buffs they are replacing
• how much time the specific Operator spends in the facility per day
• which "other" Operators you may have (can affect the first 2 bullets)
• the specific build of your base (can affect the first 2 bullets)

We provide "estimated" Sanity costs at the beginning of the sections for Operators 4★ and below (we do not for 5★ since it is our opinion that they should not be promoted for RIIC Base Skills alone).  If you would like to determine the exact "time to pay off" for your own personal situation, here are some formulas that may help:

Total Estimated Sanity Cost = (EXP_NEEDED / 7400 * 28.56) + (LMD_NEEDED / 7500 * 30) ) + Sanity Cost for Enhancement Materials

Factory Skills

Factory makes one gold bar (500 LMD) per 72 minutes = 10,000 LMD per day = 20 sanity per day.

Total LMD gained per 24 hours worked for an Operator = 10000 x Buff percentage

So, for example, Spot adds 3000 LMD per 24 hours worked, and so pays for himself after 13.25 days of being assigned to a Factory. 

So to calculate how long, in your particular case, the promotion costs will take to pay off, the formula would be the following:

Total Calendar days to pay off Operator X Promotion = Total Sanity Cost to Promote Operator X / {[(X buff percentage - buff percentage of Operator they are replacing) x 20] x number of hour worked per day} / 24

(If any of this math is incorrect, or if I am missing anything, please contact me via Discord or email.  Thanks!)

1★ and 2★ Operators gain their second Skills when they reach Level 30, making them extremely cheap to gain and therefore usually worth the expense.

• The total estimated Sanity cost to raise a 1★ or 2★ Operator from scratch to Level 30 is 65.1.

Buff gained: +30% to Battle Records (EXP) in the Factory.

Is it worth it? Absolutely. This is the 2nd highest possible % gain and a dirt-cheap upgrade cost.  The biggest challenge for most players will be recruiting him, as robots tend to be very rare.

Buff gained: +15% productivity to Factory.

Is it worth it? Probably.  It will definitely be useful for players who are running 2-5-2 or 1-5-3, as they will likely need all the Factory buffs they can get.  Her Trading Post Skill is better, though, so if you don’t need more Factory workers, this can be skipped.

3★ Operators gain their second RIIC Skill when they reach Elite 1. Thus, the investment is bit more than 1★s and 2★s, but is still relatively cheap.

• The total estimated Sanity cost to raise a 3★ Operator from scratch to E1 is 167.

Buff gained: +30% to Precious Metal (Pure Gold) in the Factory.

Is it worth it?  Absolutely.  This is the second highest % increase at a cheap 3★ price. It pays for itself over the course of 3-4 weeks.

Buff gained: +25% in the Factory.

Is it worth it? Yes. A solid factory buff, and his first Skill isn’t very useful.  If you are running 2-5-2 or 1-5-3 you will want this for sure. Like Spot, Steward will pay for himself in under a month - not to mention his combat abilities could potentially be useful as a niche low-rarity Operator due to his unique talent.

Buff gained: +80% to byproduct when processing Elite Materials.

Is it worth it? Maybe. This is one of the highest rates possible for this effect, and is matched by few others. 75% is a rate more commonly attained by Operators, including the Friend Store Operator Gavial. If the increased rate is the difference maker in a proc, it will quickly make up the costs of Catapult’s promotion.  Catapult isn't a particularly strong gameplay investment, however, so if it doesn't proc, the investment many not pay off.  Also, she has a strong Training Post buff, which is available without promotion, and many players will prefer to use her there.

Buff gained: +30% to Trading Post.

Is it worth it? Maybe. It is a good high rate for the Trading Post, but it is available from other Operators as well.  If running 2-5-2 or 1-5-3, the player may find her better used in the Factory with her first Skill, which gives a 20-25% Factory buff.

Buff gained: +25% to Trading Post and +1 to Supply Order.

Is it worth it? Probably not. Orchid’s first Skill is a 40% buff to the HR Office.  This rate isn't the best, but it is quite good. 25% or higher Trading Post skills are already quite common for no or little development cost, so Orchid will often find herself better used leashed to the HR office. 

The second RIIC Base Skills for 4★s are also gained when they reach Elite 1. The investment, therefore, is quite a bit more than 3★s but will likely be worth it over the very-long run, especially for Operators that you would level anyway to use in combat.

• The total estimated Sanity cost to raise a 4★ Operator from scratch to E1 is 281 + Materials (281 for EXP/LMD and Chips + Elite Materials).

Buff gained: +35% to Precious Metal (Pure Gold) in the Factory.

Is it worth it?  Absolutely!  This is tied for the highest Factory buff, and Gravel is a good strategic Specialist that will end up being leveled and used anyway.

Buff gained: +30% to Battle Records (EXP) in the Factory.

Is it worth it?  Absolutely.  This is the second-highest Factory buff, and she is not a bad Operator to have developed due to her useful AoE mixed damage/slow kit.

Buff gained: +35% productivity to Battle Records.

Is it worth it?  Absolutely.  Crazy good buff at relatively cheap promotion cost.  Conviction might be a meme Operator in combat, but they are the real deal in the Base.

Buff gained: When assigned to a Factory, every Trading Post makes the Factory's Precious Metal formula related productivity +20%

Is it worth it? Absolutely.  If you are running at least 2 Trading Posts, which both of the most common variants do, her bonus is an amazing +40%. Wide-Range medics aren't particularly strong combat units, but Purestream does happen to be one of the most consistent sources of the [Status Resistance] buff.  

Buff gained: +25% in the Factory.

Is it worth it?  Yes. This is a great Factory buff, and Perfumer is a strong AoE Medic whose talent makes her HP/s quite good on large maps or maps with constant HP loss, so she will likely be leveled anyway.

Buff gained: Operators that are assigned to the same Factory that increase capacity limit will add 2% productivity per +1 capacity increase. (e.g. If an Operator increases the capacity by 5, it will add 10% to productivity)

Is it worth it?  Yes. This Skill can vastly improve the productivity bonus provided by Operators with Skills that increase capacity limit.  For example,  Noir Corne and Cuora will become Top-Tier Factory Buffers, giving them both +30% total buffs.  Thus, with Cuora + Noir + Vermeil in the Factory, your total productivity increase is 30% + 30% + 16% = 76% (better than having 3 Ops with a 25% bonus).  This team of 3 likely represents an increase in productivity no matter who you have for most players.  

On top of this, Vermeil is an excellent gameplay choice in situations where her high ATK stat and multi-target Skills can be utilized to good effect.

Buff gained: +30% to Trading Post

Is it worth it?  Probably.  This is one of the best possible Trading Post buffs, so unless the player is already running their Trading Posts full-time with Ops buffing as much or more, then Mato is a good Promote. 

Buff gained: +30% to Battle Records (EXP) in the Factory.

Is it worth it?  Probably. This is the second-highest Factory buff, but Frostleaf will not be deployed often unless you lack Ranged Guards. This will pay for itself over 2-3 months but has an upfront cost of more than an entire day’s worth of Sanity.

Buff gained: +30% to the Trading Post

Is it worth it?  Probably. A great Trading Post buff at an E1 promotion cost will be an improvement for most players.  Although not a particularly strong combat Operator, she has some unique abilities that can be fun to use.

Buff gained: +80% increase in byproduct when processing elite material

Is it worth it? Maybe.  This is one of the highest rates for elite material byproduct for one of the lowest investment costs.  However, the increase is very small and very RNG dependent.  If it means the difference in creating byproduct of an expensive material, than the investment costs will be covered very quickly.  But if you don't get lucky there will be no difference at all.  On the plus side, Sussurro is a very strong ST Medic with insane healing output while her S2 is active, so she is a great choice for development, especially for new players that don't already have well developed medics.

Buff gained: Operators with 16 or less increased capacity limit gain 1% productivity per +1 increase in storage capacity; Operators with greater than 16 increased capacity limit gain 3% productivity per +1 increase in storage capacity 

Is it worth it? Maybe.  This base skill is very similar to the one possessed by Vermeil (and they don't stack).  Bubble's potential is higher with E2 Vulcan   or Bena (the only Operator skills that gives a capacity increase of over 16 at the time of this writing), but otherwise Vermeil is better.  For gameplay purposes, Bubble faces tough competition, especially with Cuora, so most players won't be investing in her for combat.  Players should consider the investment if they:

• have E2 Vulcan already, or
• don't have Vermeil AND where using capacity increasing Operators (like Noir Corne) might be better because of a lack of Operators with high productivity bonuses.

but otherwise it will likely not be worth it.

NOTE; if you are using Bubble with Vulcan E2, the third position is best filled by Bena, or if you don't have her, an Operator that gives a higher productivity buff (if enough are available) than a capacity increase buff.

Buff gained: Capacity increased by +15 when producing Battle Records.

Is it worth it? Maybe.  When combined with an E1 Vermeil, Click gives a very solid +30% to battle record production.  But many players may find their Vermeil better used producing gold Bars.  It may also depend on what other Operators or combos the player is using (for example Bubble + Vulcan)

Buff gained: +25% to clue gain in the Reception Room.

Is it worth it?  Probably not.  Gitano does have one of the best low-rarity Clue speed bonuses  (For more details see the Reception Room Guide), but clue speed increases result in such low actual return, that paying off the promotion costs could take years considering there are other very available Operators (like 12F or rope) that have clue speed buffs that don't require any investment at all. Plus, her Skill 1 buff gives +25% to Trading Post, so new players may want to use her there until they can replace her with Operators with better buffs.  AoE casters as an archetype are quite weak, and the need for them falls off sharply after midgame.  Therefore, though she might be a good option to develop for gameplay early because of swarm mechanics being more common  (and for example, she is used in a common AnniH-3 strategy), she is not a strong long-term gameplay choice.

Buff gained: +15% to drone gain in the Power Plant.

Is it worth it?  Probably not.  It is a decent Power Plant buff, but with Operators like Greyy, Lava, and Lancet also being able to provide PP buffs with no investment required, it would take far too long to pay back the promotion costs. Also, some players swear by keeping her at E0 for the lower Deploy Cost.

Buff gained: +8 capacity limit and -.25 morale reduction

Is it worth it? Probably not.  When paired with an E1 Vermeil, an E1 Beanstalk can provide a 31% bonus to the factory, which is pretty hard to beat.  But readily available Operators Noir Corne and Cuora can reach 30% without any investment at all.  That extra 1% might be tempting for min-maxers, but it would take far too long for the difference to pay off Beanstalk's promotion costs to make it worth it.

Buff gained: +30% to Trading Post

Is it worth it? Probably not.  This Trading Post buff is one of the best available. However, her first Skill gives +30% to precious metals in the Factory, which is one of the best buffs for that Facility.  Since most popular Base builds run more Factories than Trading Posts, and more Operators are available that share this Trading Post buff, most players are going to want to keep her in the Factory pumping out that gold.

Buff gained/lost:  reduces the order limit by -1 for every 10% order acquisition efficiency provided by all other Operators stationed at that Trading Post; furthermore, increases order acquisition efficiency by +4% per every 1 orders

Is it worth it? NO, not for the RIIC Skill.  It actually makes him worse in the Trading Post.  This being said, he is a strong gameplay Operator that many Doctors will want to promote despite the loss in the Trading Post.  For more detailed information on how Jaye's Base Skills work, see the following:

This is where things start to get expensive.  Promotion to Elite 2 is an expensive proposition.  It should not be prioritized for RIIC Base Skills alone, as it will take a long-ass-time to recover the costs.  However, it could possibly be a tipping point in deciding who to E2 next, or if there are no high-priority E2 candidates for gameplay purposes.  Look here for a guide on E2 priorities:

Buff gained: Moral consumed -.3 per hour of the Trading Post when with Exusiai.

Is it worth it?  Probably. Her Skill 1 Trading Post buff is the highest in the game when paired with Lappland.   She is part of the Holy Trinity of Trading Post Maximization: Exusiai, Texas, and Lappland. She is also a strong Vanguard worth E2ing eventually for the gameplay gains as well.

Buff gained: +25% in the Factory.

Is it worth it?  Probably. Ptilopsis is a popular choice for E2, and for good reason.  This buff might just be a cherry on the top, especially if you are still running 2-5-2 or 1-5-3 at that point.

Buff gained: at E2, she reduces the Trading Post efficiency of her partners to 0, but gains 45% for each, thus giving the Post a total of 90% Efficiency (the same as having 3 Operators each with 30%).  Note that she does not receive the bonus for herself. 

Is it worth it?  Probably.  She can create a very high total Trading Post Efficiency no matter who she is paired with.  She can be partnered with Operators that provide bonuses other than efficiency, like morale (Steward, Rope) or output quality (Bibeak) bonuses.  It should be noted that Bibeak's E2 skill only results in about +1.15% efficiency (source), and it does not stack with Shamare's first RIIC Skill, so the bonus is not very large.  

Another thing to consider is that, though situational, Shamare is an excellent gameplay Operator that gains strong upgrades from her promotions, so if you are going to use her, E2 promotion is a good consideration.

Buff gained: +30% in the Factory.

Is it worth it?  Maybe.  If you are planning on using this niche Operator at her full potential, then you will need to E2 her eventually.  The Skill she gains is one of the best non-specialized buff for the Factory. Since Factory buffs are always in demand, it will be a nice addition.

Buff gained: +25% in the Factory.

Is it worth it?  Maybe.  Silence is an ST Medic whose drones give her a unique range niche, but she lacks any utility other than healing, which causes her to fall behind other ST Medics in the late game that have additional utility (like Shining or Warfarin).  If you do decide to E2 her, you will get a nice Factory buff.

Buff gained: +40% in the Factory when other Operators in the Factory provide at least 40% (she matches 5% for each 5%)

Is it worth it?  Maybe.  Fast-Redeploy Specialists can be useful, but are generally not stat-dependent, and her Talent upgrade at E2 is not hugely significant.  It might be worth it if you want to maximize your very long-term production, or use her a lot.

Buff gained: +20% in the Power Plant.

Is it worth it?  Maybe. Tied with Greyy for the best Power Plant buff in the game.  She’s a decent eventual E2 candidate if she’s a part of your squad.

Buff gained: +25% in the Reception Room.

Is it worth it?  Maybe. Tied with Ch’en, Gitano, and Astesia for the highest Reception Room buff in the game.  A good Special Operator who might be considered for eventual E2 Promotion.

Buff gained: +30% in the Trading Post.

Is it worth it?  Maybe. It’s a good Trading Post buff, and Sora is a decent candidate for E2 at some point because of her unique buffing abilities.

Buff gained: +45% in the HR Office.

Is it worth it?  Maybe.  This is the strongest buff available for the HR Office, and only Eyja E2 can offer the same.  The fluffy-tailed nuker is a decent choice for E2 gameplay as well.

Buff gained: +30% in the Trading Post.

Is it worth it?  Maybe. It’s a good Trading Post buff, but Croissant is not typically extremely high on the list of 5★ Operators to E2 first.  However, if you want to maximize her Shift strength by M3ing her S2, then you will get a nice Trading Post buff along the way.

Buff gained: More like "Debuffs Removed".  The E2 skill negates the moral penalty of the E1 Skill, and also turns the capacity limit negative into a capacity limit positive.

Is it worth it?  Maybe. Her base productive of 25% isn't that impressive, but when combined with Vermeil, it jumps to 33%, which is excellent.  Asbestos is one of the best pure-Arts mitigators in the game, and has a nice improvement to her Talent at E2, so if you will use her it can be a worthy investment.

Buff gained: Factory capacity limit is increased by +12 when producing Battle Records

Is it worth it?  Maybe. If combined with Vermeil (who increases production based on capacity), Scene can contribute a LOT of productivity to a factory producing battle records.  She is a solid Summoner Supporter, especially useful in Integrated Strategies, so many doctors may want to E2 her for gameplay purposes anyway.

Buff gained: +35% to Battle Records (EXP) in the Factory.

Is it worth it? Probably not. This is the highest possible rate for a Factory buff.  However, with the extra 5% you gain as the improvement to her first Skill, it will probably take 1000 years to recoup the E2 costs.  FEater’s S2 M3 does have a very high push force, however, and although it isn’t strictly necessary, if you are interested in playing around with Push memes, this might be a bonus along the way.

Buff gained: +5% to acquisition efficiency for every 5% provided by other Operators with a maximum of 35%.

Is it worth it?  Probably not. It is definitely a high Trading Post buff, but 30% buffs are quite plentiful and relatively cheap to obtain.  As a combat Operator, there is just no reason to use her over Cliffheart or the cheaper to develop Rope.

Buff gained: +25% in the Reception Room.

Is it worth it?  Probably not. It is an extremely high Reception Room buff, but Astesia is not a particularly strong combat Operator, and is completely overshadowed by the abundantly owned Surtr.

Buff gained: +30% to Trading Post Efficiency.

Is it worth it? Probably not. This is one of the highest Trading Post buffs, but there are many other Operators that offer it as well, and who are better or cheaper candidates for promotion.  Since you will only be running 1 or 2 Trading Posts, the most you'll be likely to gain is 5% from replacing a 25% buff.  The small gain, on top of the fact that he is not a compelling E2 choice from a gameplay perspective (especially with the existence of Cuora) means it will not be worth the expense for most players.

Buff gained: Higher chance to get larger Precious Metal orders from the Trading Post.  (aka, the gold bar orders that are produced by the Trading Post are more likely to have more gold bars in them, and thus give you more LMD)

Is it worth it?  Probably not. While having more orders with more gold bars is definitely a good thing, the problem is she doesn't have an efficiency gain to go along with it.  Unfortunately, the gain she makes from larger orders is not enough to offset the loss in efficiency, as Bibeak's E2 skill only results in about +1.15% efficiency (source). Even if paired with Shamare (which removes the penalty of no efficiency), Bibeak's skill does not stack with Shamare's first skill, making the gains even smaller.  If you are inclined to micro-manage your base to maximize the output, what you can do is swap in Bibeak right before a Trade Order is produced, and then swap her out right after.  This can be more palatable when using drones to push out multiple orders.

From a gameplay perspective, Bibeak sees good gains from her E2, but not enough, (nor is she meta enough) to make her a high E2 priority.

Buff gained: Factory productivity -5%, Capacity limit +19, and moral consumed -0.15

Is it worth it?  Probably not.  Wait, why are we event talking about an Operator that provides negative productivty?  The answer to that is Vermeil, who increases productivity by 2% for every +1 increase in Capacity Limit provided by any Operators assigned to that Factory.  Thus, pairing her with an E2 Vulcan increases productivity by 33% (one of the highest Factory buffs available).

Despite this, with the improvement she would gain over alternative Operators, it would take an incredibly long time to recover the costs of her E2 promotion. From a gameplay perspective, Vulcan sees good personal gains from her E2, but she is very situational, not meta, and can easily be replaced by other Operators.  If you love using Vulcan, then this RIIC skill will provide a nice bonus, but for the average player, the costs will not be worth the gains.

Every 6★ is worth E2ing, it is just a matter of when.  As such, we’ll ignore the “Is it worth it” section and just list a few that gain notable or unique Skills.

Buff gained: +45% in the HR Office.

Notes:  As if you needed more reasons to promote her to E2.  This is the strongest buff available for the HR Office, and only Provence E2 can offer the same.

Buff gained: +35% in the Trading Post.

Notes:  Another Operator that doesn’t need an excuse to be promoted to E2, Exusiai boasts the strongest un-assisted buff for the facility in the game, tied with Snowsant.  She is part of the Holy Trinity of Trading Post Maximization: Exusiai, Texas, and Lappland.

Buff gained: +25% in the Reception Room.

Notes:  Tied with Projekt Red, Gitano, and Astesia for the highest Reception Room buff in the game.

Buff gained: +20% to Factory productivity, in the first hour and thereafter +1%per hour, up to +25%.

Notes:  Her E0 RIIC skill provides Capacity Limit +8 to the Factory and a morale reduction as well. Thus, when paired up with Vermeil, (whose skill increases productivity by 2% for every +1 increase in Capacity Limit provided by any Operators assigned to that Factory), Ceobe's total productivity increase is 41% at its maximum, the highest increase in the game (at the time of this writing).

Buff gained: increases the rate of byproducts by 40% and halves the morale reduction from recipes that cost 8 morale.

Notes:  Her E0 base Skill that removes crafting costs makes her the best value Operator to use when crafting T2 or T3 materials.  The E2 Skill improves it even more.  More info can be found here: