Ajani Vengeant is a planeswalker who's effects need loyalty counters to use. The number of loyalty counters also means how much damage he can take before he is destroyed. You cannot have more than one Ajani Vengeant on the field at once. Planeswalkers can only be targeted as you would a creature. Planeswalkers can only be targeted as you would a creature, however this card isn't destroyed by world affects from cards like Wrath of God or Mass Calcify.