Dark fire

When the Twisted Grove’s curse broke, the death-tree caught, and what took hold of it does not behave like fire. It sheds no light that most eyes can gather. Koa can catch a faint glow off it, his eyes reaching a little further up the spectrum than Mikhail’s or Aldo’s; to the other two there is nothing there to see. It gives no heat either. It radiates cold and pulls the life out of whatever stands near it, the same cold that used to come off Nancáro in the keeps.

Mikhail named it by his spellcraft and then went further and worked out what it actually is, which is not combustion at all. The tree is a dense mass of physical negative energy whose own plane has been cut away from it, and what looks like burning is that mass diffusing out into a world made mostly of the opposite. Nothing is being consumed. Something is emptying.

It spreads by ordinary means and nothing else will do it. A torch held into the dark fire will not light. A branch broken off the tree and lit with flint and steel burns like any wood for a heartbeat, gutters out, and comes back lit as dark fire, which means anyone wanting a piece of it has to stand in the sapping long enough to see the job through. The wood does not need lighting to be dangerous: even unlit, cut from that tree, it drains whoever carries it.

The party carried some out regardless, and what the wood is worth and how it has to be packed is its own matter. Days after the break the death-tree was still alight and no smaller.