User blog comment:Ein Inferno/NP Damage Comparisons/@comment-25712820-20191219213200/@comment-32377766-20191220033610

Also, the skill's multiplier to the NP's base damage is 1.56x

Buffs of different kinds are multiplicative.

Atk Up (or Defense Down on the enemy, which is additive to Atk Up) Buster Up (or Buster Resistance down on the enemy, which is additive to a Servant's Buster Up) and NP Damage Up are all multiplied by each other. Special Damage up, like Scáthach's against Divine enemies, is another multiplier, which is why (as you can see on the list) her NP damage doubles against Divine enemies.

Ibaraki's buffs are a 1.2x Atk Up and a 1.3x NP Damage Up. 1.2 x 1.3 = 1.56

Also, about Scáthach being good for bosskilling, that's because of her immense NP damage and her Evade skill. Her NP damage made the Gilgamesh challenge quest in Nero Fest easy, for example, even though she struggled to loop without crit stars. You get more crit stars and more mid-NP NP gauge regeneration from more enemies (even more if they have low HP, like many weak enemies), and you get Overkill hits on them). You also get more crit stars the more hits your NP has.

She can spam her NP twice in a row easily with double Skadi now, but it's still difficult to get her to do it a 3rd time, because her NP doesn't generate many crit stars; it only has 1 hit.