{1}{B}: Target attacking Zombie gains indestructible until end of turn. (Damage and effects that say "destroy" don't destroy it. If its toughness is 0 or less, it's still put into its owner's graveyard.)
Accursed Horde's ability can target itself while it's attacking.
The target Zombie gains indestructible for the rest of the turn, even after it stops being an attacking creature.