Precision Hits while Momento Mori is at 5, loads 1 bonus damage round
Momento Mori does massive damage to non-player enemy shields and overpenetrates targets.
Momento Mori deals increased damage against majors and bosses.
These suck. Post your idea below.
Basically PvE buffs, because I just love the weapon and would like it to be stronger to justify using it over Sleeper/Thunderlord in PvE content. In case you're wondering, the first suggestion would not break PvP because if a player has godly aim to keep MM stacks going, then he probably didn't need MM to kill you in the first place. (Rounds cannot be stacked to exceed 5 though, because you're just getting back the shot you fired.)