Favourite Enemy [VOW]

Vow Feat

You focus for 1 hour preparing yourself to fight against a creature you know. You create a vow where you choose 1 creature as your "favourite enemy", after that you will choose one of the following benefits for you:

It will have advantage attack rolls against that target.
It will reduce the target's saving throws against the techniques by your Intelligence modifier + your proficiency bonus.
However, any other creature besides your "favourite enemy" adds their proficiency bonus on saving throws against you(even if they already did), and your melee attack rolls and ranged attack rolls will be with disadvantage against them.

Even if you take this vow multiple times you cannot choose the same creature multiple times.