Efreeti Flaywind

Ordain (When you cast this spell you may tap a
creature you control that shares a color with it. If
you do, this spell becomes ordained.)
Efreeti Flaywind deals X damage to each
creature where X is equal to the number of
Deserts you control. If Efreeti Flaywind was
ordained, it can't be countered and damage it
deals can't be prevented.