So apparently if you change the targets allowed in the Incinerate spell, it stops working, for example in the map the hero can attack both ground and air units and I changed the Incinerate spell's targets allowed to both ground and air and it only worked on air.
So short story: Don't change the targets allowed.
Also download the map I made, it has fancy music and a custom spell based on Incinerate that works.
And.. Use lvl1 of the spell at first, the other levels are quite.. Overpowered.