Legendary Artifact // Legendary Land — Cave
Legendary Artifact
When Brass's Tunnel-Grinder enters, discard any number of cards, then draw that many cards plus one.
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.)
Legendary Land — Cave
(Transforms from Brass's Tunnel-Grinder.)
{T}: Add {R}.
Whenever you cast a permanent spell using mana produced by Tecutlan, discover X, where X is that spell's mana value.
This triggers when the spell is cast, before it resolves. Even if the spell is countered, the cast trigger still resolves. Copies of spells are not cast, so they won't trigger this.
If this card's activated ability produces mana and doesn't target, it's a mana ability. Mana abilities resolve immediately without using the stack — opponents can't respond to them. However, abilities that target (even if they produce mana) aren't mana abilities.