Ace has a sword. Nina has a buster arm. The JAM has his body and a built-in omnidirectional dash. While dashing, JAM's front half becomes immune to enemy collision damage (but not bullets/hazards!) and instead deals damage by crashing into his foes, bouncing backward and re-enabling his dash, allowing him to continue his assault or quickly get out of harms way before his foe's retort.
His aerial dash can be risky for combat, but also makes him a superb platformer for those who can master it.