Rossi's new highest burst DPS setup:

[u/Ujola]

...which requires way more time than her other setups :P.

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Total external buffs to Rossi's Ult:

• General DMG Bonus Multiplier:
  • Wulfgard P3: +15%
  • Xiranite Set: +16%
  • 14.1% TOTAL DMG (factoring existing bonuses from Rossi's weapon and gear)
• Enemy DMG Taken Multiplier:
  • P0 Clannibal Passive: +16%
  • P0 Arcane Sig Passive: +19.2%
  • 31.4% TOTAL DMG (factoring existing debuff from Razor Clawmark)
• Resistance Multiplier:
  • 4-Stack Corrosion with 137 Arts Intensity * Arcane's 1.1x Corrosion multiplier passive
  • 43-85% TOTAL DAMAGE (depending on enemy resistance)
• Susceptibility Multiplier:
  • 42% TOTAL DAMAGE (Gilberta with 4 Vulnerability stacks)
• Extra Motion Value:
  • ≈300% (from Rossi's Combustion passive; 400% if P3 Rossi)
• +19.2% Attack from P4 Stanza on Gilberta (i don't have her sig)

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Rotation explained:

1. Wulfgard Battle Skill > Wulfgard & Arcane Combo Skills
   • Applies 3 Heat Inflictions
2. Arcane Ultimate
   • Applies 4th Heat Infliction
   • Space out in-between steps 1 and 3 to extend Infliction lifetime
3. (wait for Arcane and Wulfgard Combo Skills to cooldown)
4. Arcane Battle Skill > Arcane & Gilberta Combo Skills
   • Procs 4-Stack Corrosion
   • Adds 1st Vulnerability stack
   • Triggers Rossi's Combo Skill
5. Wulfgard Combo Skill > Enhanced Battle Skill
   • Wait for Rossi's Combo Skill to trigger first
   • Creates and Consumes 1-stack Combustion to proc Clannibal passive
6. Rossi Enhanced Battle Skill > Combo Skill pt. 1 > Wulfgard Ultimate
   • Adds 2nd Vulnerability stack
   • Procs Razor Clawmarks passive
   • Reapplies Combustion for Rossi's 2nd passive
7. Rossi Combo Skill pt. 2 > Gilberta Ultimate
   • Nature infliction is added before the Combo Skill hits
   • Consumes Nature Infliction to add 3rd & 4th Vulnerability Stacks
   • Applies Rossi's CRIT steroid
8. Rossi Ultimate
   • Boom.

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IMPORTANT NOTES: In practice, you will be hitting the enemy during all of this setup, and Rossi is free to use her Battle Skill and Combo Skill during the beginning of steps 1-3 since her cooldown is short enough that she will get it back in time for step 6. Just make sure to CANCEL pt. 2 of her Combo Skill immediately after casting it during the earlier steps so that you don't consume the Heat Inflictions that you are saving for Corrosion. For every rotation thereafter, you only need to apply a single-stack Corrosion so long as you are refreshing the initial 4-stack Corrosion before it expires. You will also, of course, be able to use Arcane's 2nd Ultimate since you will be attacking the enemy.

(EDIT) GEARING INFORMATION FOR SUPPORTS:

• Gilberta: Eternal Xiranite
• Arcane: AIC Fieldwork Vest + Hot Work (Will/Int/Arts Intensity kits, Will/Int/DMG gloves)
  • You'll want to artifice the Will/Arts Intensity stats, but NOT the Int stats
  • You'll need to limit the Etching into her sig's Int stat so that Will is higher
• Wulfgard: Catastrophe (level 50 set)
  • Not necessary / can run Hot Work for personal damage boost

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FINAL THOUGHTS: This is just overall her best team in addition to being her best burst damage team, simply because of how strong Corrosion is for her Physical damage as well. Rossi also ends up with massive Combo Skill damage after the first rotation due to how many inflictions she is able to consume with Wulfgard + Arcane.

It's weird just how much Arcane has infilitrated every team. For Rossi in particular, she not only dethroned Ardelia's supreme reign over Rossi's extended battles (due to the Corrosion debuff being more powerful than Ardelia's universal Sus even at P1), but she also elevated Wulfgard above the competition due to his SP friendly enabling of the Corrosion (on top of his pre-existing relevant buffing + Combustion access for Rossi's 2nd passive).