Voracious Dragon

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

The List

Duel Decks: Knights vs. Dragons

Flying
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.)
When Voracious Dragon enters the battlefield, it deals damage to target creature or player equal to twice the number of Goblins it devoured.

Conflux

Flying
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.)
When Voracious Dragon comes into play, it deals damage to target creature or player equal to twice the number of Goblins it devoured.

"The number of Goblins it devoured" means "The number of Goblins sacrificed as a result of its devour ability as it entered." For each creature that Voracious Dragon devoured, this ability checks its creature type as it last existed on the battlefield to see if it was a Goblin at that time.