Backup is a triggered ability that appears in the form Backup N. When a creature with backup enters the battlefield, you choose a target creature. That creature gets N +1/+1 counters. If the target is a different creature — not the one that just entered — it also gains the ability or abilities printed after the backup reminder text until end of turn. If you target the backup creature itself, it still gets the counters, but it won’t gain the extra ability this way.
In play, backup gives you a choice: grow one of your creatures, or hand a useful keyword to another creature already on the battlefield. The counters can make a blocker bigger or push extra damage, while the temporary ability can grant evasion, protection, or another combat advantage. Because the trigger happens when the creature enters, timing matters — you choose the target as the ability resolves.
