the pets plugin lets you make any mob you kill with a lead become your pet. i'm not sure if its compatible with infernal mobs though so make a backup of the server before adding it.
Actually I've found the mypet plugin to be a very useful one... I suggested it a while back but unfortunately the idea was shot down before it got very far... ppl just don't like having pet zombehs I guess? and I think there may be plenty of them removed sooner or later [even still after the last reset with the world border thing]
