Taking hp per card would, with all the CC used, be OP, killing too fast. Having an upkeep would mean this stays on the field until destroyed, and i feel the hp per card is too much for that.
So instead of an upkeep or adding cost, give it a time limit like dim. shield.
Mhhh... i'm not sure it would be OP. Remember that it's double sided.
So, even opponent can use its effect to his advantage.
Also, in the long run this would balance the drawing power of time: more drawing, more playing, more HP spent.
I see no reason to drop the card.
And I don't think reducing a player's max HP is OP. But the point about regenerating Spells and Permanents is well taken.
I would change the text to:
When creatures are destroyed, they go to the bottom of their owner's deck. Each turn, each player's maximum health is reduced by 2.
This gives the card a dual purpose. It would stall for a very long time, and it gives an interesting strategy to players using Shard of Divinity and Stone Skin. But I don't think it would break the game at all.
I did not considered lowering maximum health, but i must admit this is the breaker of a stalemate.
But i would not give up with permanents and spells, this is the interesting part of this card!
Maybe i should consider to split this card into three cards that recycle spells, creatures and permanents.
What do you think?
EDIT: Also, i think that recycling creatures should be a
card.
Recycling spells should be a
card.
And recycling permanents a
card.