291 - Mutant Force

These guys have some of the most uninspired villain names ever, and not even in the "old school charming" kind of way.  From left to right, you've got Slither, Lifter, Peeper, Shocker, and Burner.

290 - Ms Marvel

The Ms Marvel in the Handbook was Sharon Ventura, but I went with Marvel's new Ms Marvel, Kamala Khan, instead.

289 - Morlocks

288 - Morgan Le Fay

287 - Morbius the Living Vampire

286 - Moon Knight

285 - Moondragon

284 - Molecule Man

283 - Mole Man

282 - Mojo

281 - Modred the Mystic

280 - Mockingbird

279 - Mr. Hyde

278 - Mr Fear

277 - Mr Fantastic

276 - Mirage

275 - Mesmero

274 - Merlin