If either creature is an illegal target as Garruk's second ability tries to resolve, the creature you control won't deal damage to any creature.
2020-06-23
When assigning combat damage, you choose for each creature whether you want to assign its damage to the creature blocking it, or if you want to assign it to the player or planeswalker the creature is attacking. You can't split the damage assignment between them.
2020-06-23
Garruk's last ability affects only creatures you control at the time it resolves. Creatures you begin to control later in the turn won't gain the ability.
+1: Reveal the top card of your library. If it's a creature card, put it into your hand. Otherwise, put it on the bottom of your library.
−2: Target creature you control deals damage equal to its power to another target creature.
−7: Until end of turn, creatures you control gain "You may have this creature assign its combat damage as though it weren't blocked."
