Hellkite Hatchling

Devour 1 (As this enters, you may sacrifice any number of creatures. This creature enters with that many +1/+1 counters on it.)
Hellkite Hatchling has flying and trample if it devoured a creature.

Planechase Anthology

Devour 1 (As this enters the battlefield, you may sacrifice any number of creatures. This creature enters the battlefield with that many +1/+1 counters on it.)
Hellkite Hatchling has flying and trample if it devoured a creature.

Planechase 2012

Conflux

Devour 1 (As this comes into play, you may sacrifice any number of creatures. This creature comes into play with that many +1/+1 counters on it.)
Hellkite Hatchling has flying and trample if it devoured a creature.

Hellkite Hatchling has flying and trample if at least one creature was sacrificed as a result of the Hatchling's devour ability as it entered. It retains those abilities even if its +1/+1 counters are somehow removed.

If another creature becomes a copy of Hellkite Hatchling (due to Mirrorweave, for example), the second ability checks to see whether that creature — not the original Hellkite Hatchling — devoured a creature as it entered.