H: Chord of Calling, Grave Pact W: Promo Batterskull

I have a M15 Chord of Calling and a Tenth Edition Grave Pact I'm looking to drop for a Promo Batterskull.

To me, seems fair. SCG lists the Batterskull at 20, the Grave Pact at 13, and the Chord of Calling at 10. As it stands, TCGMid is 20 for the Chord+Pact and 18 for the Skull.