Heir of the Wilds

Deathtouch
Ferocious — Whenever this creature attacks, if you control a creature with power 4 or greater, this creature gets +1/+1 until end of turn.

Magic Online Promos

In the high caves of the Qal Sisma mountains, young hunters quest to hear the echoes of their fierce ancestors.

Khans of Tarkir Promos

Khans of Tarkir

Deathtouch
Ferocious — Whenever Heir of the Wilds attacks, if you control a creature with power 4 or greater, Heir of the Wilds gets +1/+1 until end of turn.

Heir of the Wilds has a triggered ferocious ability with an intervening “if” clause. That ability will check if you control a creature with power 4 or greater whenever Heir of the Wilds attacks. If you don’t at that time, the ability won’t trigger at all. If it triggers, the ability will also check if you control a creature with power 4 or greater as it resolves. If you don’t at that time, the ability won’t do anything. Note that the creature with power 4 or greater you control as the ability triggers doesn’t necessarily have to be the same one you control as the ability resolves.