Race

Beast

Power of the Wild · levels at 2 / 4 / 6 different pieces

2
All allies, including summons, deal +10% attack damage.
4
All allies, including summons, deal another +25% attack damage (+35% in total).
6
Physical damage from your allies stacks a debuff on the target, up to 10 stacks. Each stack makes it take +10% physical damage, up to +100%.
Note: The tooltip says attacks add the stacks, but any physical damage does, including physical spells.

Official in-game tooltip

Species Trait: Power of the Wild
Active when you have at least (N) different Beast pieces on board. (Multiple effects stack)

(2) Beasts: All allies have +10% attack damage, including summoned units.
(4) Beasts: All allies have +25% attack damage, including summoned units.
(6) Beasts: Attacks from all allies increase physical damage taken by the target by 10%. This effect stacks up to a maximum of 10 and can be applied by friendly summoned units.

Beasts have superhuman strength, stamina and speed, and are good at group predation.