What you mentioned is a skill's damage coefficient, which is not what Lukrecia meant by flat damage buffs.
Lycan's Savagery applies Instinct that stacks to 25% outgoing physical damage, Howl of Terror applies Keystone Predator that increases all outgoing damage by 15%.
Pouncing Strike applies a 15% to 30% increase to target incoming damage, which is not a buff from the player, rather a debuff on the enemy.
Horc Evader applies 75% buff at the cost of -40% resistance to the player.
Dark Metal Necro's skillset returns whenever another Metal music concert is released, Rotting Riff applies Reverberating a 25% outgoing buff, Sacrificial Pact applies Cursed Echo if Reverberating is present, a stackable buff of 25% up to 3 stacks for 75% at the cost of -25% resistance to the player up to 3 stacks for 75%.
< Message edited by Legendary Ash -- 1/3/2021 16:45:23 >