Preyseizer Dragon

Flying
Devour 2 (As this creature enters, you may sacrifice any number of creatures. It enters with twice that many +1/+1 counters on it.)
Whenever this creature attacks, it deals damage to any target equal to the number of +1/+1 counters on this creature.

The List

Planechase Anthology

Flying
Devour 2 (As this enters the battlefield, you may sacrifice any number of creatures. This creature enters the battlefield with twice that many +1/+1 counters on it.)
Whenever Preyseizer Dragon attacks, it deals damage to target creature or player equal to the number of +1/+1 counters on Preyseizer Dragon.

Planechase 2012

Preyseizer Dragon's ability counts the number of +1/+1 counters on it when the ability resolves. It counts any +1/+1 counters, not just ones put on it due to devour.