Let me start off by saying I love the series and everything you have done with it. This is a good card idea. The immortal effect is very important for this card because every type of CC that attacks creature's healths would kill this. On top of that, this creature would be one of the first creature targeted by CC spells because of its ability. I think that, for at least the unupgraded, that the ability should cost two light quanta instead of one, to stop excessive use of this ability. If that were to happen, the price to play them should go down to 3/2. Another way to stop the excessive use of this ability is to have the diamond able to target each creature only once. I think that the upgraded needs to have a bigger difference from the unupgraded. To solve that, it could either become 2/1 or have the unupped skill cost two and the upped skill cost one. I could see a few decks that could use this, starting with a mono pegasus deck that uses these and blessings. I could also see a Vader Sader variation that uses these to make the daggers and crusaders heal more. This could be used to start dune scorp and deathstalker decks. This card has endless combinations. Great job with the card idea and excellent job with the card art, I liked how you made it shine the light symbol.