The match-three core is deceptively simple -- slide a row or column to zap a batch of "plops" off the screen. Knocking out one of the smiling pieces changes its background color until it finds a hue to settle on. Once you've painted the entire grid, you advance to the next level. We weren't aware of this mechanic at first, as we mistook it as a graphical glitch. You can imagine how frustrating this got towards the later, larger puzzles.
The battery on the right acts as a timer, recharging slightly with each cleared clump or combo. When the timer runs out, the level ends, sending you back a few puzzles. There are two helpful power-ups that you can get after a long chain of popped plops, one of which recharges the battery, while the other starts you off with a fresh set of pieces.
After the fifth level and an animated cutscene (!), the game starts to randomly litter the playing field with what appears to be dog poop. Contrary to common sense, bagging up the excrement is actually inadvisable, as eliminating too many of them leads to an automatic loss. Leaving too many scattered, however, severely limits your ability to clear plops.
Even at its .51 build, the puzzles are tremendously satisfying, and we highly suggest that you try Plop Invaders out. Considering that the homebrew game is available for free to play on your DS or emulator of choice, do you really have any excuse not to?