Read through the abilities.
A unique resource is always cool, but it's gotta be special. It really just seems like a more specific mana pool. Energy is a windowed resource, Rage is one built up through fighting, and Heat is something you don't always want to reach max of.
Q- Okay, but not interesting in design. Makes for a good filler ability, but probably not something you want to attach to a mage. The lack of skillshots in place for enhanced auto attacks isn't always a good thing.
W- Not exactly something useful. If you have a dash, you either want to kite, or you want to engage. He has no hard CC, so engage is out of the question, and kiting doesn't make sense unless you have quick casting spelling's and fast autos.
E- Low gameplay/counterplay. Provides something a tank would want (Standing still soaking damage) on someone that definitely doesn't want to do that.
R- Genuinely fun idea with stealth. Granted, it needs counterplay a la Rengar-esque marks so that the enemy can know that your entire team is hidden, but otherwise, stealthing an entire team is something that would be the reason you bring a champion into the game in the first place.
You're focusing too much on the thematic of shadows and not branching out into the character itself with the gameplay, and you aren't focusing on the ideas that Riot would value and that make good champions.
Satisfaction, Health, Learnability, and Thematic are all important, so don't give up, and keep designing. Remember everything you do, and apply it to newer designs or revamps.
