The Fused Trinity
The hand cannon would be a fusion of last word, thorn and ace of spades. Round would cause lasting damage (Like Thorn), increased accuracy when fired from the hip (Last Word), and reloading after a kill would grant extra-damage rounds (Ace). It also fires full auto (Last Word). Its perks when be similar to Thorn, Kills would grant orbs that, when collected by you or your teammates, increased their mobility to Stomp-E level. It would have to have a pretty big nerf, like only 9 shots and be 90 rpm, but it would still be pretty good. The quest would require you to acquire all three exotics, then go to Banshee to start the Quest. Youi would have to get 500 kills with each hand cannon. Then 25 when their perks are active. Then, a crucible bar where you must defeat guardians with one of the weapons being "fused". (Progress would go back by one point upon death) Then, complete the "Ace in the Hole" mission with different voice lines, Then return to Banshee. The catalyst quest would be a random drop after a kill, and would require 50 kills while any one of the perks are active. Then, the catalyst would require you to get "Sparks" which would randomly drop upon precision kills. Then return to Banshee. The catalyst adds the Firefly perk to the gun.