Metronome allows any Pokémon to participate as long as it can learn the move. A list of Pokémon are as follows (Fully evolved Pokémon only): Clefable, Primeape, Poliwrath, Alakazam, Machamp, Golem, Gengar, Hypno, Hitmonlee, Hitmonchan, Mr. Mime, Jynx, Snorlax, Mewtwo, Mew, Politoed, Granbull, Ursaring, Miltank, Blissey, Celebi, Hariyama, Medicham, Plusle, Minun, Volbeat, Illumise, Spinda, Kecleon, Banette, Jirachi, Togekiss, Dusknoir.
The metronome game is more about teambuilding than skill, Luck of course plays the biggest part, but a poor team will not get far. For this reason the most common Pokémon are the legendaries, alongside the more powerful, bulky Pokémon such as Machamp, Snorlax, Hariyama, Togekiss and Dusknoir. Clefable, Gengar, Golem and Blissey see degrees of use but (in all but Clefable's case, who is generally inferior to Snorlax) have poorly distributed stats, meaning that poor luck spells instant death, rather than a tough battle, as a Pokémon like Jirachi would find bad luck easier to deal with because of its well rounded stats and great typing. Dusknoir is the preferred ghost due to Pressure, and Machamp is the preferred Fighting type due to No Guard.
Other points of interest are that Mewtwo's Unnerve is banned, due to it negating Leppa Berry and forcing Struggle, hence a defensive mewtwo could rip teams apart before they should be beaten.