Hyper beam is useless against the following:
-gengar
-Gastly
-Steelix
-onix
-golem
-graveller, rhydon, Misdreavus, tyranitar, and basically anything that can withstand hyperbeam from Mew.
Stick to Mewtwo or smoething, Mew's stats are too low.
P.S: That's fissure, and that's also useless against:
-skarmory
-Nosepass
-aron(yes, aron)
-Lairon
-Aggron
Anything with sturdy.