It's good to see the good ol' fossill Muk's pokepower back in action. But as Aikyou said, too bad Muk needs to be the active Pokémon in order for it to work. And it would be a nice added effect if it prevented other Poké-bodies from working too.
Poison ring is a pretty nice attack, 20 damage, poison and prevents opponents from escaping, and for just two energies. Really useful against basic Pokémon. Sludge toss is pretty nice too, 50 damage for 3 energies isn't really too bad. The Muk could use some more HP though 7.6/10