@@unlimitoad I forgot to give you an actual answer lol Siris's Ult damage is significantly determined by her Resilience stacks (The one that maxed out at 200) Each of these stacks would boost her Thermal Damage by 0.9% (1% at M5), and she can charge up to 100 stacks consumption (120 at M1) while casting her Ult. This alone can provide her Ult up to 90% (M0) / 108% (M1) / 120% (M5) Thermal Damage boost, which is a significant amount of damage. And while we're at it, since Siris by herself already got so much Thermal Damage boost on her own, using a support that can reduce the boss' Resistance Value or increase Siris' Attack Power can ramp up her burst potential by a good amount as well. (Acacia Kaguya equipped with T5 Prismatic Igniter & Armana Logistic Set is a good example of this). Pairing Siris with Acacia Kaguya and Enya Exuvia is probably one of the more optimal burst setups for Siris right now, and I actually have seen someone dropping up to a million damage on Siris' Ult as well. So yeah, this basically is how I set up a burst for my Siris!
If you unlock Yao's M1, she can reload her Ult ammo using her Standard Skill one at a time. Also, this has synergy with her M3, where she gets 15 U-Energy refunds for each remaining bullet in her Ult form. (Either from pressing R to do a manual reload or switching to another character) At 0:32, I reload her Ult back to a full magazine before switching to Eatchel so Yao's Ult would recharge my U-energy up to 75 and allow me to reactivate her Ultimate form again once I finish breaking LoY's pillars.