Capcom Mii Costume: Roll
A second Mega Man character is often highly requested, but since we're including Leon, we won't have another Capcom character-at least, not for the first wave of DLC. Since Roll is one of the most beloved Mega Man characters to not have a Mii Costume, I'll submit her. Being Rock's brother and assistant at Light Labs, she was the third Robot Master ever made, making her very important in the series' lore. She doesn't do much in the main games, however she's had her spot in multiple MvC games and is a fan favorite character. (she was even my most wanted for a while).
EDIT: Oh, and I forgot to mention-Roll would be a Mii Swordfighter costume, using her broom as a sword.
Capcom Assist Trophy: Frank West
We already have two Capcom-based zombie hunters on our roster, but what's room for one more-at least, in Assist Trophy form? Frank West is the main character of the series Dead Rising, where you beat the absolute **** out of zombies with whatever's handy. When active, Frank West will run to the opponent at the speed of Marth's dash and use three weapons (whether or not he is in range) before despawning. These can be a lot of things, so here's a list of some of them (might flesh this out later):
Cardboard Box (Projectile, low damage, low knockback, decent range)
Nailgun (Projectile, OK damage, low knockback, good range)
Bench (Melee, high damage, good knockback)
Handgun (Projectile, high damage, high knockback, incredible range)
Lawn Mower (Melee, high damage, low knockback)
Mailbox (Melee, decent damage, great knockback)
Chair (Projectile, decent damage, OK knockback)
Water gun (Projectile, pretty weak windbox)
Television (Projectile, OK damage, good knockback)
Mega Buster (Fires a fully charged Buster shot. High damage and kills pretty early.)
Depending on how good a weapon is, it will have a higher or lower chance of being used. Cardboard box is the most common, and Mega Buster is the least common.