I'm keeping it simple here. The ideas just came to mind and I don't have the time to sort out all of the details. But here they are. - An auto rifle or a pulse rifle with a grenade launcher attachment (a mode-swap weapon). Defeating two or three enemies with the weapon loads a grenade into the launcher (max of 1) and additional kills increase the damage and maybe the blast radius of the grenade. The grenade explodes on impact. - An auto rifle with an alternate firing mode where it shoots slower but harder with explosive rounds (still full-auto). Uncertain about the conditions for the other firing mode. Perhaps it could be something like consuming your grenade or melee charge to switch to that firing mode for a short time. *- A thought about Cerberus's catalyst perk... It's still pretty lackluster. I get the idea. It's like a discount shotgun... that leaves much to be desired. Using the previous weapon idea's perk condition could work here if the alternate-fire mode's damage was increased by a decent amount (still weaker than a shotgun per shot). I don't think the activation of the mode can be left the same if the damage is buffed.