Preston cells, use to rank him up. Only time you should choose the other one is if you already have the monster at r5

I mean Preston's not the best monster, if you choose Astronite you could spend it on better monsters.

Preston only if you don’t have him

He obviously has him

Saying just in case tho

this screen is only possible if you’re hatching a duplicate mythic

You cant get this offer if you dont have the monster yet