Zool online DOS game Ninja of the Nth Dimension is a side-scrolling platform video game, which is single-player and part of the homonymous franchise. The player takes the role of a little gremlin, Zool, that is forced on planet Earth and to become a better ninja and gain some points, he has to go through some adventures in many different locations and prove himself. The gameplay is quite interesting, as it mixes the usual platform mode, as the main character has to surpass every level, collecting items and defeating final bosses at each of them, with other minigames, in arcade style, and a platform space shooter minigame and a game where, on an in-game piano, he has to play specific tunes in order to collect some points.
Wikipedia: https://en.wikipedia.org/wiki/Zool_2