If Atzocan Archer isn’t on the battlefield as its triggered ability resolves, or if the target of that ability is illegal, no creature will deal or be dealt damage.

You must choose another target creature (if able) as Atzocan Archer’s triggered ability is put on the stack. You choose as that ability resolves whether those creatures fight.

Atzocan Archer’s ability can target another creature you control (such as a Dinosaur with an enrage ability).