Turns out that MV (movement) is the only stat not used in the original rules. I'm using them for spells. It's basically a stunt that uses MV instead of AC (armor class).
1d20 + Level of Spell being attempted < MV + HD (Wizard's level)
At each new level, gain a number of spells with levels totalling the character's new level. In other words, at 2nd level, gain two 1st level spells or one 2nd level spell. At 4th level, gain one 4th level spell, or one 3rd level spell + one 1st level spell, or gain two 2nd level spells, or gain four 1st level spells.