[Marwin Luminarias]

Hmm, if Elemental Immunity Water makes the caster into water, then that's like becoming an Elemental. So Elementalists can use Elemental Essence to alter their forms now? This is especially difficult since substituting their forms using any elemental essence is going to result in a painful death.

Think about it: you are dealing with Air, Water, Fire, Earth. Imbuing yourself with any of those essences is going to hurt. It's not normal, and I don't think it's possible unless you're dealing with great amounts of power (IE Archmage level)

Elemental Immunity can simply produce a 'skin tight' layer that protects the caster from any single element. But again, back to the question, how does this allow the caster to breath under water.