I think a manipulation or necromancer class would be interesting. One grenade could mark a plot of land as inaccessible to enemies for a short time (maybe like the vestiges that Wakers of Crota drop), one could make enemies lose aggro on any marked ally (like if your buddy is being swarmed by thrall and you throw one at him, then all the thrall ignore him for a few seconds) and one could make weak enemies turn on each other. The melee would revive and convert a non-ultra enemy that it kills to your side for a short time. Upgrades could increase the time it remains, increase its attack power, or give non-major enemies a chance to become majors when revived (so that ascendant knight you punched to death has a chance to be a hallowed knight when fighting for you). The super would convert all non-ultra or major enemies in a certain range to allies, like the melee but with more potential victims. Upgrades would be more range, elemental shields on some converted enemies, and longer lives for them.