Devour X, where X is the number of creatures devoured this way (As this enters, you may sacrifice any number of creatures. This creature enters with X +1/+1 counters on it for each of those creatures.)
For example, if Thromok devours one creature, it will enter with one +1/+1 counter on it. If it devours two creatures, it will enter with two +1/+1 counters for each of them, for a total of four +1/+1 counters. Devouring three creatures will produce nine +1/+1 counters, and so on.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.