Relentless

Relentless is a talent which enables a creature to use their full attack power when attacking. When a creature with Relentless defeats a unit, any remaining unused attack power is conserved and used on the next available target; this continues until attack power is depleted. This is typically a talent of strong, high-attack creatures, as they have more attack power to spread between multiple targets. Units behind walls are especially vulnerable to the Relentless talent, because a creature with this talent can demolish a wall and continue to attack previously-defended units.

In-game description
If opponent blocking unit is destroyed, this creature will continue its attack.

Trivia

 * When used in the game's code, it's referred to as "AttackForwardContinuous".