Mechanic Idea - "Delving X"

 Temporary name: Delving X
Mechanic type: Ability Word 
Mechanic text: "Each X cards you exile from your graveyard while casting this spell pays for {1}."

Knobs:
- The amount of cards exiled for 1 mana discount
- If needed, the mechanic could be shifted to have different discounts for each spell (diminishing the modality of the card while better adjusting the discount)
- If needed, the mechanic could only work on an alternate cost (requiring more colored pips or having a larger generic mana cost that would need a discount)
- The generic cost of the spell

Innovation:
- Balancing Delve