Well, may as well post a few more pics of custom enemies and mechanics coded for the game!
More familiar bosses I need to start work on.
A demon enemy based on Mario Fusion.
Falling humanoids that explode when they hit the ground.
Metal Slug style aliens.
Bullet Bills that target Mario with dropped sprites.
A rocket/vertical rocket barrel mechanic.
Free flight levels with straight fireballs.
Zingers from the Donkey Kong Country series (other patterns in development)