Flickering polukranos

[Ekann1]

I think you can respond to it, but if polukranos leaves the battlefield before it resolves, nothing happens and it fizzles.

arn't monsterous and the ability that says "when CARDNAME becomes monsterous" two separate abilities though?

By "it" I meant the 2nd trigger. Don't know if your question has been answered enough already, but I hope this clarifies it a bit... Maybe....

[Kaleo42]

Oh. So {gift of immortality} would be a better option?

Yes assuming he dies so you can do it again.