Wario stuff:
Captain Syrup and the black sugar gang, Denpu the genie, Syrup's Castle, the S.S. Tea cup, Bobo, Dunk, DD, Cuckoo Condor, Cractus, Catbat... (pretty much all WL4 Bosses), the Music Box World, Rudy the Clown, Dr. Awero Stein, Princess Shokora (human form together with her cat form),
Wario's Car, a compilation of the standard Wario World enemies, Dual Dragon, Dinomighty, Clown-a-Round, Winter Windster (just cuz he's so delightfully creepy) and the Black Jewel (even if his design is boring).
There's SO much to choose from.
Mario stuff:
Petey Piranha (his gamecube version, not the Brawl version), Melody Pianissima, Bogmire, Sunshine's Gooper Blooper, Mario Zone (SML2), Wart, Tatanga,
Zelda stuff:
the Windfish, the Eight Instruments of the Sirens, Ricky, Dimitri & Moosh,
...that one big-hand + head boss from Minish Cap, forgot the name
uh...that's all I can think of right now.