Dragon Unit (also known as Castle of Dragon) is a side-scrolling action-adventure game in which Geraden must hack and slash his way through the kingdom and destroy legions on Darklarza's forces. Initially equipped with a sword and a shield, plus the armor on his back, Geraden can upgrade to more powerful offensive and defensive options, as well as obtain various powerful magic spells.
While the speed boost trick can't be done when playing with two players, mamuuuut still keeps things interesting with a variety of two-player antics.
We also have a run of this game using a single player.