I agree with QuantumT, this card is OP in its current form. Lets compare it to a Electrum Hourglass:
Hourglass - 4
to summon, 1
per turn to use
Pact - 2
to summon, 0 per turn to use, -5hp per turn
Pact + SoG - 2
plus 3 other to summon, 0 per turn to use
Obviously, the Hourglass is 100% obsolete if this card comes out in its current form. I would support a cost increase to 4
, and a removal of the ability to destroy it. Just like QT said, a pact is something that cannot be broken, therefore this permanent should be just that, permanent. Those modifications would nerf it enough to make it strategic, but not OP, seeing as you could easily deck out after using it too early if you get stalled a bit.