Belome, the second...
"Ack! It's a snack attack! And...YOU'RE it!!"
~ Belome

Belome's learned some new tricks, but I wouldn't sweat it. Use Toadstool and Mallow, because a) Therapy and Group Hug are invaluable b) Belome can't take the heat from Mallow's Shocker attack, and c) their clones are the easiest to defeat. Toadstool should have the Parasol, Mallow kicks Belome booty with a Ribbit Stick, and Mario gets a Troopa Shell. Keep 'em safe with Sailor clothing! Make sure they stay healthy with a Safety Ring, Safety Badge, and Wake Up Pin. If you end up head-to-head with all three clones, take Mallow's clone out first, next the evil Toadstool 2, and finally Mario's diabolical copy. Don't be surprised if Belome splits and leaves you alone with his precious clones! Just pound 'em into the ground and rejoice; Belome's flown the coop for good this time.