At first glance, Fishbane is the kind of game we've seen a lot of; a retro platformer with NES-, or maybe even 2600-level graphics and pretty good chiptune music. What makes Fishbane memorable, however, is the introduction of one novel mechanic, and the way the puzzles of the game are built around that mechanic.
Specifically, in each level you quickly get a harpoon. You can throw it left or right, into the geography of the game, thereby providing a platform on which you may jump to reach otherwise inaccessible areas. Timing throws is important, as otherwise your platform may be too high to reach, or too low to provide access to the area you're trying to reach.
The harpoon can do a number of other tricks as well, which I won't detail to avoid spoilers -- figuring out its potential uses is key to solving most of the game's puzzles. I will note that if you time a throw, jump, and run correctly, you can fly on your own harpoon.
Fishbane has three levels, so it's not that long; and while a certain platforming proficiency is called upon, its difficulty lies more in puzzlesolving than twitch mastery.