Came to report an Issue but too many clicks to reach this page.
For starters, I just played a game where a player used Angel of Something, can't remember because of too many clicks but the card text said that instead of taking damage, mill cards instead. They combined this with Gaia's Blessing which states that cards in a player's graveyard are to be shuffled back into the players deck. It doesn't require the card to be exiled or any other form of payment.
Nope, I caused damage after damage and blocked all my damage knowing they'd recoup it with unlimited life via Gaia's Blessing. It's OP and all it would take is having Gaia's Blessing Exiled after it was used and/or requiring the Angel of Something to have a mana cost to activate. Probably Both.