I dunno why I feel the need to mention this, but... How about a game-mode for the PvP that pits two guardians in a 1v1 gladiator style match. Each player would get a small number of lives, and the one left standing wins. Maps for this would be small but give a variety of options; from tight corridors, to large open arenas. Players in these modes would be matched based on their skill and level. The rewards for winning would be greater than that of a standard multiplayer match.