Devour is a flavorful, narrow mechanic from Shards of Alara (specifically Jund - Red-Black-Green - which most people don't like. (Turns out most people don't enjoy sacrificing their own stuff.) In the right context, it can be very powerful, but in order to use it you've got to understand it. Let's get into it.

Eat up!

Devour is a static ability. That means it's just... always on. It can't be turned off. (Another example would be "Flying" or "Haste".) Sure, if something comes along that removes all abilities, that will get rid of it, but a Creature with Devour (and they're all Creatures) just... always has Devour.

Devour states as the Creature with Devour enters the Battlefield, the player may sacrifice any number of Creatures to the Devouring Creature. A number of +1/+1 counters will be put on the Creature when it Enters. The number of counters is determined by the number following Devour on the card (Devour 1 means one counter per sacrifice, devour 2 means two per sacrifice, and on up the chain).

Note this is a replacement effect and not a trigger; the Creature with Devour will Enter at the larger size. So if I have a 3/3 Creature with Devour 1 and sacrifice three Creatures to its Devour ability, it will be seen as a 6/6 when it Enters.

Chow down with Devour

Jund got cards with Devour through each part of Shards of Alara block. In addition, cards have come out in a few sets since then, including Modern Horizons and Commander 2020.

Maybe the most famous card with Devour is Predator Dragon, which was often used as a finisher in a Modern deck from this era.

A 4/4 with Flying and Haste for six isn't a bad deal, but if you can sacrifice a couple of Creatures to it, adding two +1/+1 counters for each sacrifice, you've got a serious threat. Sacrifice eight Creatures? You're killing someone.

I won more than a few games of Limited in that block on the back of a couple of Thorn-Thrash Viashino, which could quickly get to dangerous levels and the ability to give it Trample made it a much bigger problem.

Thromok the Insatiable has Devour X, where you multiply the amount of Creatures you Devour by itself. If you Devour one, you get Devour 1, so one +1/+1 counter. If you Devour 4, you get Devour 4 four times, so 16 counters. Devouring 20 Goblins? That's 400 counters.

Occasionally, a Creature with Devour gets an additional ability. My favorite is Skullmulcher, which is surprisingly powerful in a Commander game where it's leveraged well.

Fell Beast of Mordor similarly has an extra effect, though it's not counting the Creatures it Devoured, but rather how many counters it has on it. Devour just gives a way to stick counters on it from the very beginning.

You hungry?

Two cards have been printed since Alara which play on the Devour basics: Caprichrome and Feasting Hobbit.

Caprichrome apparently eats metal, and Feasting Hobbit eats, well, Food, getting substantially larger for each Food it consumes.

It's also probably worth mentioning Dragon Broodmother, which doesn't have Devour herself but creates Tokens that do - each Upkeep, no less, so great for multiplayer games like Commander.

I could eat

A couple of other things worth noting.

You can choose not to Devour anything. It's not a requirement, it's an option.

You can Devour stuff no matter how the Creature with Devour Enters - it needn't be cast or come from your Hand or anything.

Devouring happens as the spell or ability which puts the Creature with Devour on the 'field resolves. That means the sacrificing of other Creatures to the ability can't be countered.

You can only sacrifice Creatures you control, which means if you have two Creatures with Devour Entering at the same time, one can't Devour the other (you don't control either yet). Similarly, you can't sacrifice the same Creature to satisfy two Devour abilities - if two Creatures with Devour are coming it at once, you can't sacrifice the same Goblin to both of them.

Let's feast

Devour is rated a 6 on the Storm Scale, and is actually considered the poster child: it has narrow design space (in fact, Emerge and Exploit are kind of plays on Devour with less-limited payoffs), people mostly don't like it, but it is really flavorful. It makes perfect sense some giant thing would come through and eat other stuff, getting stronger and more powerful along the way! In the right shell, the ability can be very strong.

Thanks for reading.