Contact me if you are having trouble balancing your game for a more specific response.
I have assisted in balancing several games that were not my own, and as a host of many dozens of games, I have a standard checklist for what is and isn't balanced.
For starters, the game must be winnable by all factions, even if the odds are against that happening.
If there is a large faction (the town/innocent team) which has two protector/doctor/defender roles, then it is entirely possible that they could simply reveal publicly and then defend each other for the rest of the game. If there is a reliable investigator, they could also both be checked out. Now it is almost impossible for these two roles to die. They won't be lynched or murdered. Add a serial killer/lone wolf role. No matter how awesome this particular role, this role will not be able to defeat the two basically bulletproof roles. And that means that the game has the potential to be broken and unwinnable for the Serial Killer role. He cannot outvote or murder the two defenders. So no matter whatever else happens, the Serial Killer will always lose to this duo in the end.
In theory you could give the Serial Killer extra voting power or the ability to somehow murder through protection, and it could possibly be balanced that way. But at the same time, the game is still fairly unbalanced because until those two roles are dead, everyone else in the game is much more suspect and liable to be voted en masse and slain at the request of the two nigh-unstoppable innocents.
Even if you made it balanced, what happens if the game events unfold in such a way that the balance is disturbed? Suppose one of the two defenders is killed right away.... in your zeal to balance the game, you've made this incredibly powerful Serial Killer who has abilities tailor-made to match your potentially unstoppable innocent duo. But that duo no longer exists.... the game has become very unbalanced because an intended element to stand up to the uber-powerful serial killer no longer exists, and the see-saw is tilted too far in the other direction for the game to be balanced. It could just end up being a one-sided slaughter, all because the game host didn't make proper preparations for the eventuality of an early power role loss.
So far:
1) Make sure the game is winnable by all sides at the start of the game.
2) If one of the balancing elements is removed early on, make sure the game is still winnable for all sides. Otherwise one wrong lynch or murder ends the game and all the suspense is sucked out of it.
Some game hosts loathe to make basic roles, so they start passing out abilities and personal goals to everyone. But after crafting some awesome abilities and personal goals for over half the players, they start running low on ideas and just throw something together at the last minute. So now you have:
LAME ROLES.
Example:
Your objective is to locate character A using your scanning power. Your scanning power is useless for anything else. Your personal goal is to make sure such and such a character doesn't die. You have the ability to protect said character one time. But since you don't know when they will be attacked, your personal goal is nigh-impossible. And it is far more likely they will die before you even find them. If you do find them, when do you protect them?
I understand personal goals where you want so-and-so to survive, or wish to outlive so-and-so. That's fine as a stand-alone, throwaway, bonus points kind of goal, but when that is all that person is focused on, and they barely have the skills to accomplish that at all, then the role is pretty weak.
It is just taking a basic standard innocent role and giving it what amounts to a bogus, unwinnable mission. As if that player's character is given busywork.... sure, lynch some scumbags, but also do my taxes. It's not very interesting, and the whole concept is forgettable.
Given the near impossibility of accomplishing that goal, it's not even worth focusing on. Meanwhile, someone else might have the inclination to kill a certain person, and have the ability to murder them outright. It's a far easier goal to accomplish. Which of the two personal goals do you think will be fulfilled by the game's end?
3) Every player in your game is important. Make sure they have realistic goals and a realistic shot at accomplishing said goals, even if it is difficult. If you give them an ultra-weak role and a lame goal and nearly no chance of accomplishing it, that person's enjoyment of the game could be affected. Meanwhile, Johnny with the powerful role and the easy goal accomplishes his task, simply because he was lucky enough to be granted the easy role.
Sometimes people make it too hard for the "evil" roles to win, by doing the following:
A) Overpowering the innocent faction
B) Limiting the powers of the guilty faction too much
C) Creating too many other evil factions who will likely destroy each other, handing the innocent team an easy victory because they are many and the evil powers are few.
Examples:
A-
TOO MANY POWERFUL ROLES
The innocent faction doesn't need to have 4 investigators. In a recent game there were too many investigators and I said that should be toned down. And I'm talking real investigators, not watcher roles or tracker roles or people who scan for items....
guilt/innocence investigators. For starters, guilt/innocence investigators suck, and they suck hard. It's unsporting. Number one, a certain group of players will always be investigated first, and when they do, and they were unfortunately randomly selected to be guilty, they've already lost the game. Simply because peeps always scan them. This has happened to me many, many times.
The only games I ever lost as a scumbag have all involved too many powerful roles (i.e.
everyone else in the game was a roleblocker [WTH???] or
everyone could see all my actions happening and they looked guilty in the writeup [WTH????] or
MULTIPLE GUILT/INNOCENCE SCANNERS [GD, FFS, WTH????] and therefore totally ruined my enjoyment of the game and the challenge of it).
People also become too reliant on guilt-innocence scanners. People don't bother looking for guilty behavior, it becomes all about mindlessly following whoever the scanner says to kill. No one hones their skills that way, and the dynamic of the game shifts totally from the uninformed majority versus an informed minority, to an informed majority versus a powerless minority. Where's the challenge?
There's also no chance of lies and tactics. How is a player that people consider good supposed to weasel out of being accused as guilty by a guilty scanner? Especially if said scanner is willing to die if they are wrong? Especially if said person isn't even the scanner, but someone speaking on their behalf? The rest of the evil faction cannot even retaliate, or when they try, it is stopped by a protector role.
Then it just becomes a game of shooting fish in a barrel. There is no tactic which can overcome it, just exceedingly lucky guesses as to who to murder. But for the evil faction to win, they shouldn't be required to kill 3-4 people in the correct order just to prevent themselves from auto-losing the game due to sheer ease.
If you're going to have all these powerful roles on the innocent side, there needs to be COMPENSATION on the evil side. For example:
- Having people who can avoid being detected by investigation
- Having the ability to protect others on your team from investigation
- Having the ability to frame innocent people if they are investigated
- Being unlynchable unless others on the team have died
- Having a vengeful lynchee power, to kill your accuser if you get lynched
- Having the ability to kill people during the day phase
- Having a suicide bombing power
- Being able to murder multiple times per night phase
- Having your results be inconclusive on the first scan, along with half of the innocent players, requiring a second scan.
- Perhaps the evil factions have the ability to send notes back and forth via the game host, anonymously.
- Having more than 3 team members.
- Having the ability to block other people's actions.
And so on.
B-
Limiting the powers of the guilty faction too much
If you cripple your guilty faction and make them underpowered, do you really expect them to win?
- Having only three members when there are multiple roles that can murder at night, possibly resulting in that team being reduced to 1 member in the first couple of rounds, and therefore unable to realistically win the game.
- Having only one member of that team have the ability to kill, and if they die, the team loses that power.
- Giving them a blocking power, but then advertising that power in the writeup and letting everyone know, at the same time, that the person using that power is most likely evil. So therefore they cannot use it against any innocent powerful role without being labeled as guilty for certain by everyone.
- Giving them limited strength and unable to kill people stronger than them, therefore making it real simple.... you just lynch anyone who wants weapons, because they are likely guilty. Then, as a topper, make it so the innocents can destroy such weapons instead of voting them to people. Furthermore, having guilt-innocence scanners check out someone who is innocent and strong, and then voting all weapons to said person, thus making them unbeatable and removing all chance of an evil victory.
- Allowing people to share role PMs but not giving the guilty parties a cover role, or allowing them to see a standard innocent role PM.
Doing this kind of stuff means you hate the people you have cursed as guilty, and you also hate the innocent players because they will have very little challenge or enjoyment when hunting the fish in the barrel you call the big bad of your game.
C- Creating too many other evil factions who will likely destroy each other, handing the innocent team an easy victory because they are many and the evil powers are few.
Oh look, you made 4 evil factions, each with only 2 players apiece, or one of them is a serial killer.
- A basic Serial Killer will not win the game, so it is a doomed role.
- The evil factions will likely end up murdering half or all of the players on opposing teams, and taking damage in the process. Now, you have a huge innocent team and one or two guilty murderers left. Add investigators and defenders and you don't even have a challenge anymore.
- Any time there are multiple evil factions, the innocent team has a great advantage and does not need lots and lots of powerful roles. I cite for you my Treehouse of Horror game, where the mafia families ended up nearly destroying the town, and then turned on each other in their quest to be the last one standing, and the endgame was literally one innocent role and two guilty roles in opposition. The town only had 1 power role, a standard investigator. They nearly won. You don't need to overload the innocent faction with power roles when the guilty parties will kill each other off.
4) Make the evil faction challenging to defeat, or at the very least, hard to find.
Don't go overboard and make a guilty faction with 6 members, or unable to kill any of the members unless they are all killed in a specific order.

No offense. Unless there's significant compensation for that on the innocent side.
5) If it is unlikely the innocent team will ever, by accident, outvote the evil faction, then the game is broken. THAT is a game where you can have a couple of innocent/guilty investigators and still have it be plausible.
Giving everyone super powers makes it no longer a game of uninformed majority versus informed minority. Then it can very easily be a game of "use a spreadsheet, have everyone reveal what they did all game long, and then deduce who is guilty simply by process of elimination".
Even if the game were "balanced" in this case, it could swiftly become unbalanced on night one.... the evil powers wipe out all the really, really powerful roles right away, making it impossible to win for the innocent team, or perhaps the innocent team murdering/blocking/defending and then easily crippling the guilty team right off the bat. Or, making everyone in your game a blocker except the guilty parties. That's just.... wrong. Please don't ever do that again.
6) Too many super roles makes the game lame.
In conclusion, don't overcomplicate things. More does not always equal better. Balance is not always achieved by adding things. The basis of this game was, as a reminder, basic innocent people versus one or two guilty people, and NO POWERS, GOALS, ITEMS, STRENGTH, etc. That formula worked. It worked because it was an uninformed majority versus an informed minority with the ability to fight back, but not have the power to get themselves out of a lynch.
If you go too far away from that, you have a different game, which is fine. NOTW is very different.
I understand this. But if you veer too far into crazy land and you make something that no longer even resembles the source material, then it is difficult to balance, and then balancing might require such drastic steps that it actually makes the game unplayable.
A recent game called riftwar on another forum gave basically everyone special powers. The end result was a giant cluster that was no longer in character, ruined the story, and ultimately made all the powers useless anyway since everyone was getting blocked and murdered or investigated or defended every night anyway.
It didn't resemble a fun, mystery oriented game anymore, it was a random, chaotic, melee with no point. What unbalances the game is adding too much to it, or not compensating for what little does get added to it.
3 basic guilty roles with 2 murders can defeat 40 basic innocent roles. It has happened before. That is balanced. That is a fun game.
Adding a detective can be interesting, but adding more.... defenders and blockers and trackers and so forth.... will unbalance the game to the innocent side. Then you have to add more guilty roles, or give the guilty roles incredible powers. And then, the game will be dominated by those with powers, and those without will feel useless and stupid. And then you get massive inactivity or nothing but boring bandwagons every round.
A good soup doesn't contain too many ingredients, and the ingredients should be carefully measured, balanced out, and necessary to the soup. Throwing tons of sugar into chicken noodle soup ruins both. Same with these games.... adding too much to a game can ruin the point of everything else you've already added to the game.
7) By now, I know what is balanced. But it takes experience or lucky guessing. But use these guidelines and a bit of logic and sense of fairness and fun for everyone, and you will succeed.
And that's my 2,500+ word essay on balancing.