Aboleth Spawn

Aboleth Spawn's ability will always go on the stack on top of the entering creature's triggered ability that caused it to trigger. The copy it creates will be created on the stack on top of the entering creature's triggered ability and the copy will resolve before that ability.

The copy will have the same targets as the ability it's copying unless you choose new ones. You may change any number of the targets, including all of them or none of them. If, for one of the targets, you can't choose a new legal target, then it remains unchanged (even if the current target is illegal).