Are you sure an ability like this is codable?
Let's say you use this to RT the opponent's creatures. What are the costs compared to Eternity?
Eternity: One card, 6|5
(if I recall correctly) + 3
per turn
Pact: Three cards (Pact+Your creature+Electrum Hourglass to do a direct comparison), 7|6
+ (2|1
+ Creature cost) per turn, lasts 3 turns
As it stands, if you use Pact exactly like Eternity, it's worse in all aspects. That said, it's more flexible than Eternity. You don't have to use Hourglass to redraw your card if you don't want to, and you can play multiple creatures a turn. For this second reason, it could Eternity lock better than the actual Eternity can, which is a problem. (If you use Photon, for example, with this, you can RT creatures from the opponent's field equal to one more than the number of Hourglasses/Nymphs you have on the field... EVERY TURN. Assuming you have the quanta for it.)
How does this work with Deja Vu, Parallel Universe, Pharaoh, etc.?
I'm thinking of a Pact/Pharaoh/SoR deck right now if the Pact works on Pharaoh.