If it's direct, simply making a counter role won't work.
Oh, town has a cop, but mafia has a godfather.
Balanced? Not exactly. It's balanced in the sense that the cop can now only kill every other mafia member easily instead of just the godfather, or that the godfather can be investigated and literally get a clear ride to victory off of a cleared cop claim.
Balance would be forcing the cop to be a target earlier on by making it to where he can't vote, has to choose an investigative target during the day phase in full view of town, has to choose someone else to get his results for him, his results are posted only after he dies (amnesia cop), etc.
or, balancing with other roles, adding in millers, other cop roles (some false), redirecting abilities, etc.
Basically, you can't ever have a direct power and assume it can't break the game. It can. This can be acceptable, but just know you can have a game with 4 scum and 8 town with one cop and 7 VTs and the one cop could win the game on his investigations alone if he didn't get NKilled.
If you have a vig and he targets mafia all 3 nights, scum loses. They're just done. A good vig choice can be awesome, but giving them free reign and them making the right choice randomly? Destroys scum balance. Likewise, giving mafia a killing ability and giving town only one or two power roles to balance things can lead to a lynch to one and a kill to other.
Gauge how much randomness you are wiling to allow, then pick a few "core roles" in the game you know you want to have, and then simply play damage control with the rest.
Some of the roles in this game, like spider-man and superman, were meant only to give a strong townie a good ability to make them feel safe to play as a strong townie (even though spidey was hidden maf) while others like Colossus and The Tick were meant to be sacrificial roles that help Town at the expense of their own player slot.
TL;DR, make as few direct things as possible. Is he a vig? WHEN can he be a vig and what does he need to do. Is he a mafia member? How does he mesh with the other mafia members? How much do they need their partners and do they fall apart if one dies randomly?
Takes a lot of thought and planning, but watering down roles or making them very difficult to use is generally a way of self balancing.