Here are a few more ideas.
Detons - Zeeky H Bomb, or a face of Leonidas from The 300 that yells "THIS IS SPARTAAA!" when it chases you.
Buzzes - Ships from Star Trek are all I can think of.
Jetty-Syn Bomber - I've got a really funny idea for this. It involves a bloke on a flying toilet that basically craps on you.
Jetty-Syn Gunner - Possibly a Cacodemon from the Doom series.
Skim - Someone on a toilet boat that also craps on you.
Pop-up Turret - A Homer Simpson that pops up from the floor and fires lasers at you. Yes, crap idea.
Mario enemies - REPLACE THEM WITH NAZIS AND REPLACE BOWSER WITH HITLER!!! *shot*
Also, I think I may have a better idea for a backstory for this... random thing. It takes place in the Sonic universe to keep the SRB2 flavour but with a twist. Well, here goes.
Sonic and his freinds are having a break from their adventures when suddenly Eggman appeared. Or so they thought it was. Sonic noticed that he was wearing fancier clothes and said, "What the hell Eggman? Why are you wearing those stinking fancy clothes?! I hope this is a really retarded disguise you're wearing!" However, the Eggman lookalike said, "You dare insult me, you nincompoop? I am not that silly cousin of mine, I am Master Crumpetman!" Sonic then has what appeared to be a WTF expression on his face, but Crumpetman continued, "Indubitably, I will turn the whole of Mobius into a gigantic ballroom, gain infinite tea and crumpets and I will rid of the horribly rude people such as you! And with this, nothing shall ever stop me!" "What the heck is 'this'?!" Sonic answered, but as he looked on he saw a dimensional tear in time and space! "My servants will soon come to this planet! Meet your most terrible end, indeed!" and as Crumpetman said that, many strange things which appear to be from other dimensions have been unleashed onto the planet Mobius, and Sonic must fight them, take advantage of the power-ups form other dimensions and defeat the evil and little known cousin of Dr. Eggman named Master Crumpetman and stop his plans of a fancy world domination!