Which villains could be involved in the prison break arc?
A small thread:

I don't think Shiggy is going to need All For One anymore, he taught him everything. And as we've seen, he needs no more barriers and might possibly have his quirk. In this moment he could steal every important quirk from AFO like Search, making him an even better AFO.

Shigaraki is the face of the Liberation Army, and with the prison break arc he could gain even more dangerous followers.
However, not everyone might be on shiggy's side. One if them might be the Hero Killer, Stain.

His ideals are not of liberation. He wants to correct society, to make everyone remember the true meaning of a hero.
Nobody listened to his ideals, so he started killing heroes he considered fake.

The Paranormal Liberation Front follows the very essence of Destro's ideals: No longer being held back by society's standards.
And where's the perfect place to start the first big move into society? Exactly, Tartarus.

As mentioned, current Villains in Tartarus include Muscular, Moonfish, Overhaul and Kurogiri. No word on Gentle or the Hassaikai. From this list, Overhaul is the least likely to be influenced, as he can't use his quirk. Could he have a different role? Unlikely. He's lost purpose.

Essentially Shigaraki would be repeating AFO's story, but with a bigger impact. The ideals of liberation bring people obscured by society to his side, and with Dabi as an endorser of Stain's will.. Everything can come crashing down.

Shigaraki, a kid turned villain because he was rejected by society.
Dabi, 'killed' and left to rot in the darkest parts of the streets.
Twice, joined the league because nobody else accepted him.
Gentle, committed a heavy casualty and forced to embrace evil.

The idea of breaking into Tartarus itself would attract a lot of attention from the media, but if they want to make an even bigger impact, there's only one time.

Remember when All Might said he was going to meet Stain? You know where this is going.

If they killed Toshinori, the former symbol of peace would be forever destroyed. Endeavor and the entire Hero Commission could be heavily affected if Shigaraki and Dabi's story come to light, thus ruining hero society and spreading the ideals of liberation and fake heroes.

I think that's all I can say from this thread! Read Vigilantes as well!