At the beginning of your end step, if you descended this turn, put a bore counter on Brass s Tunnel-Grinder. Then if there are three or more bore counters on it, remove those counters and transform it. (You descended if a permanent card was put into your graveyard from anywhere.)

Tecutlan, the Searing Rift

(Transforms from Brass s Tunnel-Grinder.)

T: Add R.

Whenever you cast a permanent spell using mana produced by Tecutlan, the Searing Rift, discover X, where X is that spell s mana value.