1. Does this make things that already increase your max hp increase this more? Aka, a Divinity Shard gives 24 HP and 48 Max HP?
2. If you use miracle with this at say, 65/196 Max HP, would you jump up to 195/326 HP because you technically healed 135?
3. What is the percent chance for blindness?
As for being UP, remember that it can be used in a deck with no creatures that can be affected. Truthfully, the card is probably OP rather than UP (ironically your fix for the UP really helps reign in the OP a bit). The deck it can be useful to this degree in is the aforementioned 500 HP deck, which gets turned into a nightmarishly powerful stall. It lets you replace the earth with more light for Miracles, get up to 500 Max HP easier with huge Miracle Jumps, and also blinds all opponents for 2 turns to reduce incoming damage even more.
The major problem is that this card is really powerful in exactly one deck, and otherwise weak. might be slightly useful as colorless AoE control to stalls, but otherwise isn't that useful.