Mutant Mudds Deluxe

At the bottom of the level select screen is a mirror looking thing. Press up in front of it (like you're using a door) to go to the spooky world. Beat all of these stages and you'll unlock the trophy. (there are 20 stages, one sprite for beating each one)

These stages can get pretty difficult since you can't kill enemies outside of a few certain situations. Having the power-ups helps IMMENSELY here, and I'd recommend unlocking Grannie first since she can use all power-ups at once. You'll unlock Grannie when you get the trophy. To use her, back out to the title screen and press up on the d-pad.