Frostboil Snarl

The reveal mechanic is a specific answer to a problem the check-lands could not solve. A check-land looks at what is already on the battlefield: cast it on turn one and it enters tapped, because you have nothing to reveal it against. This design flips the source of information. It reads your hand instead of the board, so it can come in untapped on turn one as long as you are holding a card with the Island or Mountain type, exactly the moment the check-land is at its worst. The tradeoff is symmetrical to the check-land's, just mirrored across the game: the check-land punishes fast hands and rewards developed boards, while this one rewards a full grip and punishes an empty one, so it tends to falter in the late game precisely when a thinned hand has nothing left to reveal. It is the same untapped-or-tapped decision, hung on a different piece of information. That the condition keys off the Island and Mountain subtypes rather than the colors is worth noting: any card carrying those types satisfies the reveal (a shockland, a triome, a dual all qualify) even when you would never tap it for the color you want. As fixing its rate is unremarkable; as design it is a deliberate reframing of when a tapland gets to decide whether it arrives ready.