Why the prisoner is very powerfull now? Because some passives are too much powerfull, especialy siege (who destroy all your strategy based on beneficial effects/talismants) and the troll's magma shield (who burn 50% of hp of all your team) ... This is why i use the prisoner, just for counter the blue bat and the troll, any problems with other characters!
In the future update blue bat and troll will be nerf in the same time so it will not really a problem to no more use the prisoner...
Another problem with the prisoner can be that he has no counter... just let his passive works for 100% of opponents but set it as beneficial effect (can be counter with immunity) that will balance his OPness and don't totally castrate him as i've read here
And why not the same thing for siege and all the other passives? Please let us the option to counter them with immunity instead of nerfing all the premium characters in the game...