Now that we know Undertaker is NOT immune to hacked (nice one, SP), it makes me think about what kind of monster could be introduced to counter the most OP monster in the game.

If Hackster is a...hacker, then his counter must be some kind of computer technician (designed like a monster, obviously) whose job is prevent hacking taking place.

His trait could be Immune to Hacked and Stun (although Hackster can still deny him with Timestop), and he could have a move that gives immunity to hacked (but not stun) to allies.

Free Subscription - deals low physical damage
For A Year - deals low magic damage

Overtime - deals moderate magic damage
PayDay - deals low special damage
Time And A Half - deals moderate special damage, 50% chance of making target miss next turn (timestop)

Taste Of Your Own Medicine - deals moderate magic damage, removes positive effects from target
Crashed Browser - deals moderate special damage, may make target miss turn (timestop)
Norton 360 - deals low special damage to all enemies, gains life regeneration for all allies

Unlucky Mouse - deals heavy magic damage, gives immunity to hacked to all allies
Upgraded Software - deals moderate special damage to all allies, removes all negative effects from all allies
Battery Pack - deals moderate magic damage, gains stamina regeneration

Another idea: what about a monster whose skills are based on BEING possessed/hacked? So, his attacking skills target his allies, his supportive skills target enemies, etc. That way, when he's possessed/hacked/confused, he's actually a brutal attacker, but until then, he's no good? And maybe has a self-skill to possess himself? That'd be an interesting monster that would completely negate all possession abilities, more interesting than simple immunity, in my opinion.

My idea: self-target skill to possess himself and give himself double damage (Maybe an extra turn instead? Not sure there, extra turns can OP a monster). I'd give this one a single turn cooldown, so you don't use it twice in a row and you quickly have it again if you need to repossess yourself.

Then he has some high damage skills, both AoE and single targets, but they only target allies (meaning you won't use this skill unless the monster is possessed/hacked/confused). They could throw in some negative status effects if some sort if desired. Most possessions last only one turn, so you'd want his damage to be sufficiently high for it be of any real value.

A skill that gives a single enemy immunity to possession (again, you'd only want to use it when possessed). It could be AoE, but then he'd guaranteed have possession immunity and you don't want that. With a single target, it's more likely that you'll give it to a random ally than giving it to himself (although that's still a possibility).

Maybe skills that clear all negative status effects from all enemies and/or clear all good effects from all allies.

His trait obviously couldn't be immune to possession. And you wouldn't want any hardened or tough either, because you'd want the possession to land.

As I said, he'd only be worth anything when possessed. But the interesting part is you'd also have no control which skill got used and what target got hit. So the skills would need to be a bit OP'ed in order to balance the lack of control.