Sapbringer

{g}: Put a sap counter on Sapbringer.
{t}, remove X sap counters from Sapbringer: add
X mana in any combination of colors to your
mana pool.
When you tap Sapbringer to pay for a convoke
cost, it pays for an additional {x}, where X is half
the amount of sap counters on Sapbringer,
rounded down.