Munchkin Zombies question: helper negates a monster advantage?

[Bogie1494]

Situation: Player A is level 9 and has a mojo but no powers. They draw a monster (I cannot recall which and don't have the set to look at) whom gets a +3 against players without powers. After Players B-E are finished messing with it and the subsequent +3 bonus, Player A cannot defeat said monster. Player F, also level 9, offers to help defeat the monster (secretly he hold Brain Enough for Two and plans to use it to get the winning level as well). After the second round of messing with the combat by B-E, another monster and enhancers/ one-shots have been added to tie the Munchkins' Combat strengths still counting the +3 bonus for the original monster about fighting a Munchkin with no powers.

Argument: Players A and F argue that since Player F has a power they win since in actuality the +3 bonus is now negated and the monster side is now losing. B-E loudly declare scandal and cheating and bending of rules and won't allow it. Which is correct?

Side-Argument: (In player F's head, he wonders if he could actually use Brain Enough for Two to get a winning level).