It would ruin Imu's image way too much if Usopp straight up beats her himself but I have been supporting the idea that Usopp will play a crucial role against Imu. My theory was that Imu is a god of fear and feeds off of it like Moriah feeds on shadows or Big Mom feeds on shadows, all of them growing stronger from it...
Basically, as long as there are people on the battlefield who fear Imu, her powers are near infinite and if Usopp wills into existence the embodiment of Bravery, he could end up with ability like superior version Belo Betty's power, boosting the morale of the troops and people would stop fearing Imu, bringing her down to her actual power level.
You do have a point with Usopp being the one who takes out those with broken hax powers and they happen to be female characters...
I thought about this thing yesterday, if Zoro and Loki clash, Loki might overpower him with the hammer, if he doesn't use aCoC.
Even with aCoC, Loki's hammer might not be a thing one approaches by blocking...
The options are certainly interesting in the Underworld.
Pretty much, Pranks exist to do things that Oda doesn't wanna do to Shanks.
They are probably around the same power level with same type of abilities and combat style.
So, portrayal-wise, whoever beats Pranks can be considered stronger than Shanks as well.
Also, I doubt Luffy vs Pranks, the man is a swordsman after all. I simply cant picture Luffy beating a swordsman.
Unless Pranks forgets that he is a swordsman in Luffy's presence.
I think Pranks will WIFI-diff Luffy, making use of the Luffy's naivety and being off guard when he sees Shanks-like figure.
That is if Zoro doesn't step in to protect him, which in this case I would forgive Zori for not doing.
Zoro vs Pranks is more likely, IMO while Luffy will end up facing Loki, when he wakes up from the WIFI-diff...