Full analysis
Like many units lately, her skill comes in 2 parts, a passive and an active. They’re getting annoying to explain.
Her passive increases her own firepower by 5% additively for every debuff currently applied to S-ACR, letting her to slightly counteract their downsides. Night battles’ accuracy penalty does not count. The number of buffs seems to be in real time, so they leave once the debuffs wear off. Also the damage increase is applied after armor for some reason instead of before like most sane firepower buff skills. Please don’t cripple your own team to try to add units that kind of synergize with her though, since the benefits are too small to be worth it.
Steyr’s active debuffs her rate of fire, movespeed, and evasion. Then it buffs her damage, accuracy, and critical damage. The 3 debuffs also interact with her passive to give an additional 15% damage. Fortunately, 2 of the debuffs are things that ARs almost never care about in the first place: move speed and evasion, because they do the shooting and not the dodging. Then she cuts into her massive 91 base rate of fire as a penalty.