Demi is not a good spell to have, and you can have a lot by playing cards anyways. Gesper card can be refined into a black hole, wich can be refined into 30 Demis. Gesper card is a low level card that it is used fairly often.
I think that it is even one of the first cards you get.
Anyways, junction Meltdown or protect in Vit, cast protect, he can be hit with slow as well (but it is hard to make it stick.)