Additional/Made up roles in Resistance or Resistance avalon
Here's a few we like to play with. Names are a work in progress, and you do have to think through how you combine these roles, some combinations can be unbalanced. Also, for some reason most of these are Good Characters.
Oracle (Nimueh)
Ability: Once per round, (or once at the start of the game), can look at a single characters card.
Best In: Large games, where 5 cards isn't enough to know everything.
Options:

If Evil kills Nimueh instead of Merlin, it's a draw.
Instead of looking at a card, can look at one token a player in a mission has put.
Could be an Evil player as well. Note: This requires some balancing, because otherwise seeing Merlin's card is an instant win. Best is Oracle has separate win conditions: Wins by Failing Enough Missions, but Loses if Merlin dies.

King Arthur
Ability: At the start of the game, reveals his card. Is a Good player.
Best In: Smaller games, where his help in winning missions is cancelled out by making it easier to guess who Merlin is.
Options:

Limited number of missions he can take part in. (One or Two is best)
If he is on a losing mission, can no longer join missions. (Or, Good loses)

Witch
Ability: Once per game, can change a Fail token to Success. However, the next turn, one Success Token is changed to Fail
Best In: Any game, but can be a bit OP in combo with Arthur.
Options:

Sees tokens first, then changes.
Can also change a Success to Fail first, and then change a Fail to Success at any later turn.
Is an extra assigned role, meaning may be a Good or Evil character, or and one with another Role.

Cupid
Ability: At the start of the game, chooses two people to be lovers. Lovers see each others Character Cards. If Good falls in love with Evil, then the Good player wins if Evil does.
Best In: Any game
Options:

Instead of a Cupid character, start with a random pairing.
Evil converts to Good because of love.

Sir Robin
Ability: Is a Good Player, but can only play Fail Tokens.
Best In: Random Roles, i.e there may or may not be a Sir Robin in the game.
The Rat
Ability: Is an Evil Player. When included in a mission, after all tokens have been played, the rat can look at the tokens and change his if he wants.
Best In: Medium to Large games, where he won't be able to use his ability too many times.