Upon downloading Special Stage from the Add-On Content Menus, it'll show up in Time Attack. Stage Start. I love the color scheme here.
There's lots of enemies from the main game here and pits to fall in.
Wily Stage 1 enemies. You're pretty much forced to use Weapons of some sort.
Plant Mid-Boss from Hornetman's Stage.
Boulder Mid-Boss from Jewelman's Stage.
Elephant Mid-Boss from Concreteman's Stage. You'll only fight one here with a Green Ball.
Changkey Dragon Mid-Boss from Magmaman's Stage.
Big Weapon Energy.
Shark Ship Boss from Wily Stage 2. This is it for reused Bosses.
Enemies and Item pickups.
You might of seen more than one of these in the Ending of the Main game. He was actually planned to be a Boss in the Normal game, but ended up being recycled as a DLC Boss the last I heard about it.
He isn't very hard once you get the timing down. He'll run and jump around and fight round bullets at you. Jewel Satellite is his Weakness upon hitting him with it, but you could also reflect the bullets right back at him, but that only takes off 1 peg as if you were shooting the regular Rock Buster at him. Another strategy that's good incase you run out of J. Satellite is to use Magma Bazooka for the 3-way shot out of it to take 3 pegs off.
Once you defeat him you'll get a Clear Time. Unlike future games and their more than one Special Stages, you don't gain any Special Weapon upon beating him. It's kind of odd that there's an empty space in the Sub Menu for Weapons.