If there's one thing I've learned over the years, it's never gamble with an elf. I don't know how they do it, but if you put your gold down, it's as good as gone.
A very useful spell, maximum Luck makes the target creature or hero take 1/3 less damage than they otherwise would. It also cancels the effect of Misfortune. This is a high-priority spell for you melee creatures or heroes in the early game, though casting Summon Leprechaun has essentially the same effect, and you get a bonus creature stack with that spell, so it is a better spell to cast.
Unlike Stoneskin and other physical-damage reduction spells, having maximum luck reduces damage from hostile spells, as well as from attacks.