The Fortify spell is unlocked from the Genie's Palace (Castle 3). It is a spell that increases your Castle's health. Every Fortify that is cast will give less health than the previous one, according to the description. The Fortify spell costs 2 to cast.
Because the fortify restores less castle health every time it is used, a table below represents a tournament level (level 9) statistics on how efficient every additional time the fortify is used. This is assuming you have one fortify in your deck because when you have two, it appears that a fortify counts as half a use when determinating the deterioration of the card. There is a point where Extra Crystal restores more health than fortifies.
|Fortifies #||Fortify Benefit||Effeciency|
|2016||Introduction of Fortify|
|21st June 2017||Balance-Change||