i think what Mikuki has is the tester version of the cursed seal. they said the items used in the stuff he drank very similar to stuff he was making back when he left the village years ago. seem like oro used him to help advance his skill at cursed seal. after all practice makes perfect ;-) and a second thought Mikuki not so bad ass i woudl waste a good curse seal on him lol. maybe oro gave him the tester to Mikuki would gain power and seek him out for more, also seem this one seems weaker and likely not to kill him out right.

the formlua Mikuki drank might wear off after some time, idk for sure teh change might be a perment change.
i think oro might be trying to find a way to give water down seal version to all his followers so to make them more equal footing wither ninja from villages.

it took 4 sounds ninjas to take out 2 leaf village ninjas and it left them wiped for a while.
oro troops while strong never seem equal to ninja from other vilalges so far besides kimiaro (the bone blood line limit guy) and kubuto his right hand man. so far the they only good ninjas he had before sasuke.