You finish the support action before any creatures deal damage. Creatures that get a +1/+1 counter will deal damage to the creature an opponent controls, if applicable.

As Nissa’s Judgment resolves, if at least one of its targets is still legal, it will resolve, affecting only targets that are still legal at that time. If none of its targets are still legal at that time, it won’t resolve and none of its effects will happen.

You can’t put more than one +1/+1 counter on any one target using the support action.

Support can target a creature you don’t control.

If a spell with support has other abilities that target creatures, those abilities and the support ability can target the same creature.