Yes, Doc. Mercy drops the infinity, and like the above poster said, the drop rate is one of the lowest I've seen. I've read somewhere that it was something akin to .8%, but it could be wrong. Though it seems rather accurate considering he hasn't dropped one for me in the past two days, heh.
The quickest way to farm him would be flying up to his little perch from one of the geysers near the Fast Travel station. There are probably guides that teach you how to do this, but it's rather simple to figure out for yourself. Just angle yourself correctly and you can land right beside him. Have fun, heh.
Infinite pistol wont help much with hyperius BTW Get yourself refill baby maker (1.0reload speed +26% reload speed) + the 30/70 tediore relic + 55k amps bee And I prefer using Maggie for bots if he manages to summon them but the baby maker should do 5 mil minimum simply walk up to him and fire one shot toss rinse and repeat til he's dead wont "ale 20 seconds at most