GG Ironeye and Raider. The reason I stood still for a while at the beginning of the city is because my controller died. Regardless, I've made a discovery, it's better to use only the first two attacks of Corpse Piler on Rob when you have restore FP on successive attacks. Attack 1 deals 2 hits and attack 2 deals 3 hits for a total of 5, which seems to trigger the FP recovery. The last attack only deals 1 hit and is therefore a waste of FP. That's the reason I was able to spam it so much, I barely lost any FP on each use.
Pic related was my reward.