I fight my brutal AI roster with these.
Yuki Morikawa (SOS) This character was the reason why I came back to mugen in 2015. After playing The Queen of Heart 99 I thought I use her in mugen. To my surprise she doesn't play exactly the same as she does in the source game. You can beat many characters after you mastered her. She has an infinite but it's really hard to pull off and not worth going for in a match.
Rina Ogata (Maruta) She's from the same game as Yuki Morikawa and also plays differently from the source game. She is stronger than Yuki because she has beaten characters that were impossible for Yuki to beat. Since she doesn't have damage scaling her combo does a lot of damage. (For some reason using her sweep makes the combo do less damage) She has an infinite in the corner.
Petra Johanna Lagerkvist (Ina) She was in my original roster back in 2013 but I didn't know how to use her at first. Now that I'm a pro with her it's safe to say this is my strongest character (If you don't count the broken Anna) While she doesn't have an infinite and is not free from damage scaling like Rina, she can still beat every character that Rina could beat and at the same time defeating characters that was impossible for Rina. The best Arcana to use for most matches is Anutpada/Time.
Shannon (SXVector) The tallest character I use. Pretty much the only thing she has going for is her lightning super. The damage output on her normals and combo is low and it can be hard for her to gain meter on enemies that blocks and counter every normal attack. But once she gets meter she can use an unblockable super five times in one use and deal a lot of damage.
Saki Mitonoya (chikuchikugonzalez) Since she wasn't made by ZSM she has a three meter bar. I haven't fought my whole roster with Saki yet but she looks like a good character. Her Sierra assist can act as a front line defense and if she gets a hit Saki can run up to the opponent and combo them. I have a feeling she might be better than Yuki.
Maori Kasuga (Ahuron) She's not as strong as Petra by Ina damage wise and lacks time arcana but I can see potential in her being strong especially with metal Arcana. I can't do the metal Arcana super that powers up the shield and make it take two hits consistently. If I can spam that then the enemies on my roster might have trouble getting a hit on her. I would rather set that super to one button because I don't like the input.
Kagerou Imaizumi (Minoo) She has really short standing jabs and her trademark move (the one where she turns into a wolf) does little damage. For some odd reason the creator decided to make her projectile cost meter even though it does almost no damage. To make up for that she has a move where makes her gain meter if it hits the opponent. Shes a low damage character until you pull off her combo and can keep hitting the opponent to death if they don't air recover out of it.
Sousou/Karin (suigin) I never played the source game but I did managed to learn how to use this character after a lot of practice. She looks like a character with a huge learning curve and is hard to use but not useless because I still some hard characters with her. Shes's more on the weak side because no air block, slow mobility, fireball is not fullscreen, low damage unless you get a fatal counter. Fatal counter is useless against characters that reads your buttons because to get a fatal counter you need to land a counter hit with her heavy attacks or that crouching move that summons a tornado. She has a roll that can get her out of the corner but I was never able to do it again because I don't know how I did it.
Sunny Milk (Hetyo) Sunny Milk has Luna Child and Star Sapphire has strikers. I find Luna Child only useful for her healing when I'm faraway from the opponent and camping because Star Sapphire has better attacks and doesn't spawn in the front and get hit by the opponent often.
Dark Magician Girl (Tsubaki) I use to think she was useless after she lost her invincibility on her super and the crouching projectile but after putting in more practice, I figured out how to use her and beat hard characters like Master Morrigan and Hinako Shijou by Ogko Ogwo. Two characters that I never see people fight against.
Chomper (N-Mario) He's my original Mugen main. He can't block but he's really strong. He's weakness is he can't do anything in the air so if the opponent keeps hitting him and not let him touch the ground he's pretty much dead.