It fits with the lore to alter people in the game. That is what the fallen are afterall. They were once human and then turned into abominations by dark magic. The spells we do have for altering heroes are a bit lacking, but on the right track. They function fine, but offer no imagination of what is being changed about the unit. I would like each level 4 spellbook to offer a spell that connects a unit to that element. With the new code we got in beta 4, you can prevent these from stacking with each other so that once you are one with the earth, there is no chance to become one with the air.
Earth Element Infusion: +50% Defense, Gains Earthquake as an ability (which requires no mana, but has a cooldown), +3 levels to summons.
Air Element Infusion: +5 Initiative, +1 Moves, +50% Lightning Resistance.
Water Element Infusion: +50% Cold Resistance, +25% Damage to water spells.
Fire Element Infusion: +50% Fire Resistance, +25% damage to fire spells.
With a cost of 400 or so Mana and a level 4 spellbook prereq, this would be a welcome addition to the current life and death permanent buffs.