If a creature with undying already has a +1/+1 counter on it when it dies, does undying still trigger?

Undying reads: 'When this creature dies, if it had no +1/+1 counters on it, return it to the battlefield under its owner's control with a +1/+1 counter on it.' The key condition is checked at the moment the creature dies — specifically, whether it had no +1/+1 counters on it as it left the battlefield.

Per CR 702.93a, undying's triggered ability checks the game state at the time the creature died. If the creature had one or more +1/+1 counters on it at that moment, the condition is not met, the ability does not trigger, and the creature stays in the graveyard.

This is also affected by CR 603.4, which governs how triggered abilities check conditions — the 'if' clause is evaluated at the time the trigger would go on the stack, looking back at the moment of the event (death). If the condition wasn't true at that moment, the ability simply doesn't trigger.

Concrete example: You control a Strangleroot Geist (which has undying) that has received a +1/+1 counter from a spell like Hunger of the Howlpack. If it then dies, it already had a +1/+1 counter, so undying does NOT trigger and Strangleroot Geist goes to the graveyard and stays there.

Note: If the creature had only -1/-1 counters or other counter types, those do not satisfy the condition — only +1/+1 counters matter for undying's check.