Brane Food
This unsubtle assassination tool is banned in most planes of existence for being remarkably indiscriminate. Brane Food is essentially a magically mutated form of the cashew apple that has been further been manipulated in space-time until it’s just plain wrong. Then it gets steeped in a pool of evil for a week or two. When it starts to bubble and look for a victim, congratulations; the Brane Food is ready.
Brane Food works by being frighteningly appealing to human brains. Extremely so. So extremely so that the brain will itself attempt to break through its own skull and ‘attack’ the Brane Food. This, of course, never actually happens except under the highest of magical background levels; which is good, because the sight of a disembodied brain flopping around with two eyestalks while trying to crawl to its quarry is a sight that most people don’t want in their heads.
What typically happens instead is that the brain merely beats itself to death on the inside of its skull. This is less painful than it sounds, but it’s an absolutely horrible way to die and there’s no real defense against it besides not being within five feet of the Brane Food. Worse, there’s no reliable way to selectively target an individual. Even getting the damn stuff into a magically shielded box in the first place isn’t easy unless a golem is used, or something.
All of which is why Brane Food is aggressively banned, and getting caught with some is a good way to get executed. But the results are still, as they say, thorough. Resurrecting somebody after his brain has attempted to escape via his ear canal can be fairly tricky. Particularly since nobody really wants to get too close to the victim.
One last note: some people may be curious as to what happens if the brain does manage to get to the Brane Food. Well: nothing. Nothing at all. Brains don’t have mouths, after all.