If my opponent plays creature swap and gives me a Nimble Momonga and the attacks it who will gain the 1000 life points?

thanks,

Mokey

Your opponent would get the 1000 life points he/she would also then be able to search there deck for additional Nimble Momongas to special summon on there side of the field.

to add on, the reason why is because when the Nimble is destroyed it goes to the Original controllers graveyard, since it was his card and Nimble has a graveyard activation effect.