Mosasaur, Dinosaur Eater

mosasaurus costs {1} less for each creature your opponents' control and can't be countered if
you control 5 or more dinosaurs
flash, Trample, Islandwalk, Shroud
When Mosasaur, Dinosaur Eater enters the battlefield counter target spell with converted mana cost X
Mosasaur, Dinosaur Eater enters the battlefield with X +1/+1 counters on it