I too am of the opinion it needs a buff. It just isn't used in any competitive PvP decks, at all, and I honestly can't see a deck to use it in besides Aether rush which isn't really ever used. And even then immortal, due to its high cost, isn't really a rush card.
What about this? Give it the following skill:
Material Exchange
: Immortal loses 1 hp (gains +0/-1). Any Dimensional Shields in play gain 1 turn. This skill can only be used a single time per turn.
Or
Material Exchange
: Immortal loses 1 hp (gains +0/-1). All of your immaterial creatures gain +1/+0.
Or
Material Exchange
: Any Dimensional Shields in play gain 1 turn. Lobotomize Immortal.