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.