oh.. what type of mechanics?
disclaimer, this isn't to tell anyone else their hosting or whatever is wrong, im just letting you know how we do it/the games we want to play/etc
to give a more specific answer to this since i'm bored and so there's a lack of ambiguity:
let's start with
deathproof or lynch immunities lynches are town's greatest weapon. as long as they're on the same page, if they can find scum together and either hit a majority or generate the largest amount of votes and manage to lynch scum then, by day's end, they should get scum. by offering immunities to lynches you are actively punishing town for getting the right answer. "oh but they can just get him another way", but they shouldn't have to after they've collaborated in the first place to get the right answer. the basics of mafia is town working together to lynch the bad guys. successfully doing that but failing is punishing town for good play.
let's move onto to something related,
hidden vote manipulation key word is hidden. as long as it shows up in the host vote count it doesn't matter. town can work around that. town can see that there's shenanigans going on. the moment the host posts a vote count that isn't accurate then they're lying. the host is deceiving you and you can't trust the host. again the day lynch is town's greatest tool to finding scum and the one based on the most skill as it's solving on your own merits. if you think you're about to lynch a guy but suddenly they're not lynched because 10 votes is actually 8 votes and the other guy who had 7 votes is now at 9 votes then it feels defeating as you couldn't have accounted for that.
(this doesn't apply to things like executioner, governor, etc that are all submitted to the host and affect a singular day phase and doesn't require the host to deceive/lie to the players. even these roles should be limited to a singular shot and not have multiple ones in game as you shouldn't be fucking around with multiple day phases as it all comes back to the day lynch being town's greatest tool and way of solving.
again, in relation to lying to town,
allowing mafia to post things into writeups/alter role flips/anything of that sort the utility is way too high and again the players shouldn't expect the hosts to be lying to them. all these things are pretty easily seen as bastardized. death millers fall under the same line of thought. a jester is also rewarded for doing something that generally everyone is trying to avoid and isn't really too difficult to achieve in the first place.
mafia receiving additional night kills this is just massive game swining. i talked with odo about it and he used it in a way that, as a lot of people and you yourself do, can remove two high value targets at the very start of the game. whether it be high value players or high valuable roles.
alternatively you can wait to see use it to swing mid game or you can use it to end the game one phase sooner than the expected lylo. as town generally operate with a rough idea of when the split is this can have massive consequences. twice the killing power, even if it's just one additional shot, can do a lot of damage.
then there's general balancing ideas. if mafia has a janitor you don't give town a gravedigger/reviver. why? because mafia uses the janitor to get a safe claim to fake(probably because they have claims themselves that generally won't be safe to claim like we had in odo's game, so the janitor gives the mafia team a safe fake while also throwing shade onto a lot of town power roles as it could always be a scum janitor claim). if town has a gravedigger or reviver then they just revive the janitored player and suddenly that is no longer applicable. if you want to keep those roles in the gam then you just say there's a restriction that they can't use it on a janitored player, but obviously you don't want to give it free will.
mafia in general need an ability to roleblock or rolecop town to find power roles. it isn't to make the same setup every game, there are variations you can put in, but those roles are generally crucial to their night actions in countering what town is doing or trying to do.
you don't give mafia/town the same role as then mafia will just get counterclaimed and either lose their guy first or lose their guy after they lose the other guy. generally try to avoiding a situation where town gets a far greater chance of being believed over the mafia claim(for instance in our game i disagree that odo made the miller the jailkeeper as it made it impossible to contest, which i know he wasn't going for but ya i think that was a mistake).
you don't want town to have too many cop like roles as 1) they're lame as fuck 2) they kind of ruin all deception and ability to deceive by mafia. a cop or cop esque role is standard. just don't put in a bunch of them that will decimate scum on their own(cop, gunsmith, lie detector, etc). these roles have no penalties to use and are just either a free scum catch or a free town confirm).
similar idea applies to track/watchers. if you put in a bunch of motion detecting roles then they'll generally fuck up scum by sheer ability to confirm what happened every night while also being able to catch mafia in lies if they try to fake usage while also finding killers/sk in late game scenarios. also,
@CraigPelton disagrees, but watcher generally is a protective role in application. scum are going to avoid shooting someone they think will be watched. players ask for watcher on them to deter scum from using abilities or killing them.
I could go on really, but just so people stop saying we're too vague/that we're making it up on the fly.
