What does Hiruzen's monkey do?

[Rikodou Mode]

it does serve as a boss summon, by its unparalleled striking power.
as well:

- it can use staff henge & shadow clones
- then change its width & length at an exponential rate, instantaneously
- it has carbonate strength durability
- it can form an unbreakable cage or an impenetrable wall
- it is a master of taijutsu
- it is several times stronger & more agile than any base human/shinobi
- it has a remarkable sense of smell, (as does hiruzen)
- it is ridiculously badass & serves as a king of some sort

Sorry but Amaterasu is enough to stop it

 

[ultraChalk]

It was a waste to not have him transform in Edo form.