Here's an interesting thought. Could I drop him off of Mallah, then using the Book of the Skull, drop Nul's hammer to give him willpower? Well, of course you could, the real question is, what happens to the hammer when Brain is ko'd? Does it stay on the card when Mallah reattaches it? I think it should. Because I am thinking a fun combo would be Angrir's hammer on Mallah and Nul's on the Brain.

While it'd be a cool thought, no, it doesn't stay on the card at all, as the Brain no longer exists and, therefore, cannot be assigned a hammer. He's not Merging to become a Duo figure with Mallah, which is how you would be able to transfer the Hammer. Although Brain is a bystander, and therefore can be assigned the Hammer, he does not have a character card of his own; neither the Monsieur Mallah figure name nor Real Name: Mallah indicate Brain on there, which means it is not the Brain's card and would not remain. My thought is that your opponent would score 3 points.