Photon Baby is an excellent puzzle platformer, with NES-ish graphics and an interesting puzzle style. You play a little fellow with a sort of gun; while babysitting, the child you were caring for was kidnapped by a vampire bat, and you evidently have to fight through thirty platform levels featuring vampires and bats to get the brat back.
Vampires wear differently colored capes; some surfaces of each level are colored lines. You bullets are gray when fired, but take on the color of one of these lines; and a vampire can only be killed by a bullet the color of his or her cape. This is where the puzzle aspect comes in; you must figure out how to slay each vampire, given the organization of the level, and the positions of the colored lines.
The controls are quite simple; move with WASD or arrow keys, aim and shoot with the mouse. In addition, holding the space bar makes bullets move to the location of the mouse pointer, so you can drag bullets where you need them and release them.
At later levels, some cape colors do not match any of the colored lines; you need to bounce a bullet through two, different lines to change it by the laws of color combination. Sometimes more than two, in fact.
It's a nicely tuned game, with the difficulty ramping up over time; the difficulty is less in the platforming, which is straightforward, than in enemy evasion and figuring out solutions to the puzzles.
For a freeware game, it's quite polished, with very nice level design.