It totally depends on stats purely and moves you teach each Pokemon and since arceus can change its type if it were a type psychic types beat like poison mewtwo would dominate on the other hand if your arceus was a strong dark type mewtwo would fall easily.
arceus
Arceus.
Arceus.
Arceus
Well Arceus is better because is the Pokemon god
mewto
Darkrai is better. Arceus sucks! PS Dialga is the strongest!
definitly arceus he is the one who made the Pokemon universe
ZEKROM!
You can catch MEWTWO ,not Mewto, at the end of Cerulean cave
No Arceus is one of the best Pokemon exept from Pokemon indigo(online game)
arceus or mewtwo arceus is the god of pokemon and i dont know who is better because they never fought