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Hello and welcome to this Law of Ascension - Support Comparison!
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I hope I'll be able to help you, let's start!
✦ Table of contents ✦
Short Introduction
Current LoA Valkyries
Support Buff Comparison
DMG Comparison
Conclusion
✦ Short Introduction ✦
The Astral Ring Specialization [Law of Ascension] was introduced in 8.0 with Reign Solaris. It focuses on quick switch teams and QTEs with the Stellar Outburst activating special QTEs called "Stellar Shifts". For more details, you can read this guide:
Currently we have 3 battlesuits that are protected by Law of Ascension and therefore can act as main DMG dealer and Support:
PS - Peregrine Sword - Li Sushang
FWS - Ba-Dum! Fiery Wishing Star - Kiana Kaslana
RS - Reign Solaris - Durandal
Additionally 4 more battlesuits can support this Specialization:
HoH - Herrscher of Human: Ego - Elysia
TFM - Thousand-Faced Maestro: Cameo! - Sparkle
LP - Lone Planetfarer - Vita
JDS - Jovial Deception: Shadowdimmer - Songque
Having 6 support options while only needing 2 of course opens a lot of team options, so let's take a closer look to figure out which are the best teams~
✦ Current LoA Valkyries ✦
To start off let's take a quick look at the requirements each individual LoA DMG dealer has to their team and then what buffs generally are wanted~
✧ Peregrine Sword ✧
Physical - BIO
Notes on the team selection:
✧ Sushang is a Bleed DMG dealer and therefore doesn't profit from Crit or melee/ranged attacks.
✧ If another Physical character is on the team: +6% Bleed DMG
✧ If she is in Physical Breaker state: +13% Bleed DMG, +22% Total DMG
✧ She has 55% self Impair, Impair does not stack
=> Wanted buffs: Physical DMG, Physical DMG taken, Physical Breach (!), Total DMG, Total DMG taken, Bleed DMG, Bleed DMG taken
Due to her Bleed ability she's a very niche case in terms of supports, so allow me to just spoiler:
Vita + Kiana for highest DMG
Vita + Sparkle for fast rotations (if Sparkle doesn't lack SP first rot)
✧ Ba-Dum! Fiery Wishing Star ✧
Fire - Stardust
Notes on the team selection:
✧ If she is in Elemental Breaker state: Fire DMG +25%, Total DMG +6%
✧ As she is usually used against Stardust enemies, Songque's instant break point is notable
✧ Elemental DMG can't crit
=> Wanted buffs: Fire/Elemental DMG, Fire/Elemental DMG taken, Elemental Breach, Total DMG, Total DMG taken
✧ Reign Solaris ✧
Physical - Imaginary
Notes on the team selection:
✧ Durandal has enough Crit Rate to not need any additional Crit Rate from Supports
✧ Durandal has 55% self Impair, Impair does not stack
=> Wanted buffs: Physical DMG, Physical DMG taken, Physical Breach, Total DMG, Total DMG taken, Crit DMG
✧ General Hints ✧
Summary: Buffs spread on many different scaling is better than to focus on one scaling, Vulnerability and especially Breach buffs are more valuable buffs due to how rare they are.
Full version:
In Honkai Impact different scalings are calculated independently of each other, which is why you want to not focus your buffs on one stat but spread them over many different ones.
As example: Your Ba-Dum's Basic ATK deals 1000 DMG
(Option 1) you give her 100% Fire DMG
➔ 1000 * (100% + 100%) = 1000 * 2 = 2000 DMG
(Option 2) you give her 50% Fire DMG and 50% Total DMG
➔ 1000 * (100% + 50%) * (100% + 50%) = 1000 * 1,5 * 1,5 = 2250 DMG
So the more different scalings the better~
Additionally most characters have mostly Elemental/Physical DMG and Total DMG as their self buffs.
For example Ba-Dum has following self buffs in her kit and gears (only counting buffs that affect all attacks):
✧ 243% Fire/Elemental DMG
✧ 123% Total DMG
✧ 62% Fire/Elemental DMG taken
✧ 40% Total DMG taken
As you can see vulnerability buffs are way more than basic Elemental DMG or Total DMG and that counts for all characters, making Supports who give a lot of vulnerability worth more than Supports who give a lot of Elemental/Total DMG.
Additionally self Breach is extremely rare, making Breach in Supports very valuable. Ba-Dum's only self Breach is 6% for her Basic ATK.
Impair or Elemental/Physical Breaker states do not stack and you can have one buff of each at max (self-Breach excluded). As every P2 Physical DMG dealer so far has Impair, Impair doesn't have any value in Supports currently.
For highest efficiency you want to add two supports that either balance out each other's weaknesses or two Valkyries who don't show huge weaknesses in their buffs.
✦ Support Buff Comparison ✦
✧ Peregrine Sword ✧
Strengths:
✧ By far the highest Physical and Elemental vulnerability (for the leader)
✧ Highest Total DMG
Weaknesses:
✧ Underwhelming buffs for characters other than the leader, focus on leader support
✧ Low Physical DMG
➔ Sushang's main strength are abysses in which the leader's DMG is especially relevant as she mainly buffs the leader of a party.
But also in other cases she is a pretty strong support.
✧ Ba-Dum! Fiery Wishing Star ✧
Strengths:
✧ Highest Physical DMG vulnerability
✧ During Stellar Outburst high Elemental DMG vulnerability (2 out of 7)
✧ Especially Strong for Fire DMG dealers
✧ All stats are pretty average, allowing you to buff many different scalings
Weaknesses:
✧ Average Non-SO rotation time (4 out of 7), but long SO rotation (6 out of 7)
➔ Kiana is a really good all-around Support, offering different scalings. If we get another LoA Fire Valkyrie in the future she'll definitely support them even more well.
✧ Herrscher of Human: Ego ✧
Strengths:
✧ Highest Elemental DMG and high Physical DMG
✧ Only LoA Ice Support
✧ Fastest Non-So rotation
Weaknesses:
✧ Pretty much every stat besides Elemental and Physical DMG is extremely underwhelming
✧ Lowest Total DMG, Physical vulnerability and Elemental vulnerability
✧ Strengths are focused on less relevant stats as most Valkyries already have good self buffs in these multipliers
➔ She's honestly the worst LoA support so far. Her only use are Symphony abysses due to her Ice typing.
✧ Reign Solaris ✧
Strengths:
✧ Highest Total DMG taken (shared with Songque)
✧ Highest Crit DMG
✧ Offers Shield Break (65%)
Weaknesses:
✧ Rather low Elemental and Physical vulnerability
➔ Currently a rather good support. She offers high Shield Break making her a top choice against shielded enemies as well as stun trauma for Stun abysses (the single one that exists).
✧ Thousand-Faced Maestro: Cameo! ✧
Strengths:
✧ Fastest rotations
✧ Offers SP and Ultimate CD reduction
✧ Buffs are spread into different multipliers
Weaknesses:
✧ Needs SS or an early SP pack to not have SP issues, lacking SP increases her rotation length by ~2s
➔ While Sparkle's buffs aren't as insane as others, but she offers additional Ultimates and very fast rotations. This makes her extremely valuable, especially at low Disturbance when DMG isn't as required.
However, below SS she sometimes cannot use the strength of fast rotations properly due to SP lacking.
✧ Lone Planetfarer ✧
Strengths:
✧ Vita is the only character to offer Physical and Elemental Breaker state
✧ These states can activate additional buffs some characters get from their kits when in these states (Sushang/Kiana)
Weaknesses:
✧ Extremely long rotations
✧ All buffs besides Breach are underwhelming and extremely low
➔ Vita gets carried by her Breach states, allowing her to stick out. Her rotations are long and she doesn't really offer anything besides that. Especially for characters that get additional buffs from being in Breach stances she's still one of the best choices.
✧ Jovial Deception: Shadowdimmer ✧
Strengths:
✧ Highest Total DMG taken (shared with Durandal)
✧ She instantly triggers SD-enemies' first Critical Value
Weaknesses:
✧ Doesn't really stick out in anything
➔ Songque is pretty good, but not as strong as others. For SD enemies she'll always be best in slot due to her special ability to get to the first Critical Value quickly.
✦ DMG Comparison ✦
Notes: These numbers are not always accurate and can differ based on the stage you're fighting. All tests were on a typeless enemy and include one AR Charing and one Stellar Outburst rotation.
All characters are S0 with a Sync 1 weapon except for Ba-Dum who is S2 since I can't downrank her. S1 and S2 only affect her personal DMG, so the difference isn't big.
✧ Fire DMG Dealer ✧
Team: Ba-Dum! Fiery Wishing Star / Supports / Theresa AstralOP (SS)
Will add a prettier version soon
Please note:
✧ Rotation times might be ~1s faster/slower, the times are based on the in game timer
✧ Sparkle rotations can be reduced by ~2s when not needing a Combo ATK to get her first Ultimate
✧ Kiana gains additional buffs when having Elemental Breach, making Vita even better than usually
✧ Physical DMG Dealer ✧
Team: Reign Solaris / Supports / Theresa AstralOP (SS)
Please note:
✧ Rotation times might be ~1s faster/slower, the times are based on the in game timer
✧ Sparkle rotations can be reduced by ~2s when not needing a Combo ATK to get her first Ultimate
✧ Kiana is S2 while others are only at S0, this only increases her personal DMG but expect S0 to be slightly worse.
✧ Analysis ✧
! Kiana and Durandal only serve as examples to get an idea about the general strength of the Supports and results for future characters might differ !
Vita clearly falls behind in Durandal teams, DMG and rotation length wise. In Kiana's teams this is prevented thanks to her skill giving additional buffs in Elemental Breaker state.
Considering Sushang has this too we can probably expect it to be a common thing for future Valkyries.
The best team will depend on your specific abyss and wether you need fast rotations, high DMG or a mix, but let me pick out some teams deserving a special mention:
Kiana:
Vita / Durandal - Highest DMG output per rotation
Vita / Sparkle - High DMG while lowering the rotation length
Durandal / Sparkle - Best non-Vita team
Durandal:
Kiana / Sparkle - With enough SP on Sparkle probably her best team
Kiana / Songque - Highest DMG output per rotation, especially in Physical abysses
Sushang / Sparkle - Good time/DMG ratio
I hope this can give you a main idea, when unsure you can look out for the weather and boss type to see if any support benefits from that.
✦ Conclusion ✦
All Supports somewhere have their benefits, but the right Support selection can help you a lot when clearing content~
I'd like to especially point out Vita as the only Breach provider of LoA and Sparkle for having very fast rotations. I can generally recommend pulling Vita due to her ability to support 3 different Astral Rings.
As second support you can just pick out the best you have then, please refer to the tests above for reference~
Please keep in mind that the choice can differ based on the stage you're fighting though!
I would've recorded an abyss comparison but they still didn't increase Beta disturbance and at 480D the fastest rotation will easily be the best one so RIP 
- Thanks to Cyxo and Alpaca for the pictures of Valkyrie icons and such!
- Love to Inari
- Website for official wallpapers in case you're interested, here
Thank you for reading my guide, I hope I was able to help you!
Have a great day and fun with your Law of Ascension Valkyries~ 
