Card sounds may differ from in-game as they get updated.
Infiltrate - The special ability of a unit with Infiltrate occurs the first time that unit hits the enemy player. It doesn't work while the unit is on defense, such as when it is attacked by a Relic Weapon.
Overwhelm - A unit or spell with Overwhelm will deal any excess damage to your opponent on your turn (does not work while blocking).
Berserk - Units with Berserk can make a special double attack one time: If it survives the first round of battle, it will attack again. This can only be used once, and gives the unit Reckless.