Clockwork Hydra enters with four +1/+1 counters on it.
Whenever Clockwork Hydra attacks or blocks, remove a +1/+1 counter from it. If you do, Clockwork Hydra deals 1 damage to any target. : Put a +1/+1 counter on Clockwork Hydra.
If the chosen target is an illegal target by the time Clockwork Hydra's triggered ability tries to resolve, the ability doesn't resolve. You don't remove a counter from Clockwork Hydra.
19-03-2021
wotc
If Clockwork Hydra leaves the battlefield while its trigger is on the stack, you can't remove a +1/+1 counter from it, so it won't deal damage.
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.