This is my tier list I have made for all M&M character so far in all game modes.
Bierce (A) – Back in the day she was pretty bad when her speed was bellow average, but now when she is fast enough, I would say she is the best counter to Clown Gremlin and his ultimate, which are considered to be the most problematic in Maze escape. She collects a lot of shards and makes a big impact. Her ultimate is also very good. Heavy attack heals the other mortals, but that doesn't usually turn the game and doesn't do something amazing, but it's usable.
Doug Houser (C) – He's not bad, just outclassed (other balanced mortals are generally better). The only thing that makes him not go in D is the fact that his ultimate helps you escape when the portal opens because since the last update he teleports very close to the portal.
Evans (S) – Even after the nerf he's still easily the best mortal in Maze escape. He's not quite as broken as he was, but if there are 2 or 3 Evans' in the game, the monster has almost no chance (except myb Clown Gremlin can counter that). We all know the reason for that is his ultimate. You don't even have to go for the kill. Just stunning the monster for 7 seconds is amazing.
Vince & Borisov (B) – They are solid characters and really the best counter to speed monsters (myb along with Evans). They are not top tier because they don't make a huge impact when it comes to collecting shards and killing the monster doesn't make you win the game directly, but they are a good distraction and it's never a bad idea to have one of them in the game. In Maze escape I would say Vince and Borisov are equally good.
Nikson (A) – Honestly, I would almost put him in B, but let's keep him in A. We all know how awesome his ultimate is, but I have noticed he's a little bit overrated here in Maze escape. He has one problem and unfortunately it's not a small problem. Among all mortals, he has the hardest time escaping. When I play as a monster and the portal opens, I have a strategy to let others escape, but keep Nikson away. Once the portal opens, his ultimate does absolutely nothing that can help you escape. Your only chance is to get something great from item boxes (which is sometimes unreliable) or hope that the monster makes a mistake. I have put him in A just because of the huge impact on collecting shards.
Penpen (B) – And here it is… If you are a beginner in this game, let's say bellow level 5, STAY AWAY FROM PENPEN, I'M BEGGING YOU (especially in Maze escape where you will screw up the whole team). She's basically a high risk-high reward character. If a player really knows what he's doing, she can actually be in A considering how hard she is to catch. Her main weakness are speed monsters or more precisely their ultimates which she handles very bad. The penalty for her death is of course the biggest drawback. Again, if played by experienced player who knows exactly what he's doing, she is pretty good.
Murder Monkey (C) – The same thing as Doug Houser, he's outclassed. He might be a little underrated, but he doesn't do as good as other balanced monsters. His ultimate is pretty good, but high level players will know how to play around it by going through him and trying to disorient him. Overall, he's not bad, but there is always a better choice.
Agatha (A) – She's a very effective monster, especially if there is no power mortals or Evans. Some players consider her ultimate to be kinda dull, but it's actually one of the best in the game and the main reason for this is that it doesn't give you the opportunity to react to it (you have about 0,2 sec if you have a shield) and plus it will get value regardless of where you are so you can activate it whenever and wherever you want. She's a good option and it's not hard to play as her, you can definitely win a lot of games with her, but she has some counters.
Gold Watcher & Malak (B) – They are not as good as A or S characters, but they do have some good values. Their main issue is their low speed which means your playstyle has to be „sneaky“, hiding around the corners and searching for good items in item boxes to make your job more effective. Their ultimates are both really good and it depends on you individually who you prefer; less damage, but easy to aim (GW) or more damage, but harder to aim (Malak).
Dread Ducky (B) – I used to underrate this character, but it's really not bad. Its long range light attack seems to do a lot and not to mention the ultimate which is also very solid because you are almost guaranteed to get a kill. Also it is pretty easy to play as Dread Ducky and you can give your opponents a lot of trouble. For some reason I feel like Dread Ducky is one of the hardest monsters to escape when the portal opens. I would almost put it in A, but it's definitely counterable, that's not even a question.
Clown Gremlin (S) – Oh here is the one… If you get in the match where there is no Bierce or PenPen, in some cases you can literarily camp at one of the item boxes and spam your ultimate which will finish the game for you (it's not always the case, but definitely doable). His ultimate's description says his clones last for 25 seconds, but they actually last for 45. I honestly think that should be changed as soon as possible because it's really OP. Even if they nerf his ultimate, it would still be one of the best ones and the reason is exactly the same as with Agatha; you can get a value of it as soon as it's charged regardless of any situation. Now you can just spam it and win the game. Not to mention that his heavy attack is long range which makes him even better. As I said, Bierce is the best counter to him and myb PenPen if the player is careful enough, but overall he's the best monster in Maze escape. (He's the best counter to Evans.)
Brute (A) – Everything the same as GW and Malak, but I do consider his ultimate to be better than theirs. His ultimate makes a lot of damage just like theirs, but the fact that he can outrun every single character with it (except PenPen's ultimate) really makes him shine more. It's much harder to escape it than the other two. Also he can't be frozen or slowed down. Overall, amazing. Still, pretty slow otherwise and that's why he's not in S.
Fiend (A) – Yes, he's very very good, but not as powerful as people think. He is the same as Agatha, but his ultimate on the first sight seems much better. If you think outside of the box, that's not really true 100% because again, you have no way to react to Agatha, but if you hold a shield you will be warned that Fiend will teleport you and you can use it to prevent yourself from dying. Honestly, his ultimate is a mystery to me. I have noticed that the range doesn't matter, but also he sometimes doesn't teleport the weakest player, but rather the closest one. (Please let me know in the comments if you know exactly how it works). When his ultimate gets value, it is better than Agatha's. His special ability is that he pulls his target closer when he does a heavy attack, but this sounds better than it actually is. In reality it's not hard to play around it once you get hang of it. Again, a very good monster, but has the same problems as Agatha and he's a little bit overrated.
Murder Monkey (C) – I really wish he was better… In Shard mayhem it's even easier to counter him and I don't think it's ever worth running him. Sorry monkey… (Again, if you have been playing as him for a long time, you might discover some tricks to make better results, but I think other monsters just do it better.)
Agatha & Fiend (S) – Even though they are not OP, hands down, they win most of the time if they are played by the good player. Considering their speed is the highest, they can really collect the most shards and it's usually the battle between speed characters. (I might be wrong, but for what I have seen for the time I have played this game, it turns out that way.)
Gold Watcher & Malak (B) – If you run them and you are trying to collect the most shards without fighting, you are not going to win. Your main source of getting shards are kills which I honestly don't find very reliable, but if the player knows how to do it effectively, I can't complain about these two.
Dread Ducky (B) – Just like in Maze escape, nothing specific to add. It can collect a solid amount of shards, but you should get a few kills in order to win. I you know how to do it properly, it's a good option.
Clown Gremlin (A) – He's still very very good, but not as good as in Maze escape. Your clones do some kills for you, though not as many as in ME. He's a good option and you can definitely win games. (Everything else is said in the previous section.)
Brute (A) – The same as GW and Malak, but with better ultimate. I can put him in B, but I see him win more than the other two, so let's keep him in A.
Bierce (A) – Everything I said previously. She can collect a very solid amount of shards and sometimes even kill the players.
Doug Houser (C) – In this mode his ultimate again doesn't have a lot of value. He has an average speed and can collect some shards, but I don't remember seeing him perform quite well.
Evans (A) – Not as good as in Maze escape because in Soul collection when you kill someone, you just reduce their amount of shards, but you don't get any of them, so that's a small drawback. He's still pretty good though.
Vince (D) – Well, I think nobody should ever have business running Vince in Soul collection. First of all, you are slower than average and you are supposed to fight other players, but as I said, you don't get those shards when you kill them. Unlike power monster in Shard mayhem that have ultimates which help them kill someone even when they can't outrun them, first of all if you are smart, you will never try to fight Vince and even if they do try to fight you and you activate your ultimate, they will just run away and you won't be able to catch them. Enough said, Vince is really the worst mortal for Soul collection.
Nikson (S) – Hands down, this is the only case in this game where there is absolutely no counter to a character. Nikson is 100% broken, especially now when they increased the amount of shards on the map. And please, don't tell me you should just kill him a lot of times and he won't win. Guys, there are over 400 shards on the map and when a 2nd wave of shards comes, he will collect around 120 shards. Think about it. In order to make him lose those shards, he should get killed 5 times. And plus he will manage to collect some more when he's running around. Not to mention he will use his ultimate more than once. We can talk about it for hours… Broken, broken, absolutely broken. I'm happy devs announced he will be nerfed, but I'm afraid in that case he will be pretty bad in Maze escape (unless he has different features in different modes, but that would be kinda lame tbh). The only situation where you have a chance against Nikson is if he's played by a beginner, otherwise no chance.
Penpen (B) – Everything is already said about her. The good thing here is that everyone plays individually so if a player dies, he screws up himself, not the whole team.
Borisov (B) – Unlike Vince, Borisov is a competitive character in this mode. His low speed is a big drawback, but his ultimate allows him to fight other players and kill them, reducing their score. Again, I wish you could get those shards, but unfortunately you don't. If you could get them, Borisov would myb even end up in A, but this way he has a safe place in B.