Enlist is an attack trigger. When a creature with enlist attacks, you may tap a nonattacking creature you control that doesn't have summoning sickness. If you do, the attacking creature gets +X/+0 until end of turn, where X is the power of the tapped creature. The tapped creature stays tapped, so you're trading its potential block or future attack for a bigger hit now.
In play, enlist turns your board into a resource. It rewards having extra creatures, especially high-power ones that might not be attacking. You can push through more damage, win a combat against a bigger blocker, or force your opponent into tough blocking choices. Because it happens on attack, it's a combat trick that can swing a race. It appears on cards in White, Red, and Green.
