Well, Grolnok, the Omnivore was pretty much your only true frog payoff card for a while
Showcase Magnified Showcase Dossier Borderless Cards Extended Art Full-Art Impossible Basic Lands Special Guests Murders at Karlov Manor is scheduled to release on February 9
As MTG Rocks noted, the Nazgul uncommon is actually tough to find in collector's booster packs, and most of all, for flavor reasons, this card has nine different versions of its illustration to represent the actual Nazgul characters
Putting one or more land cards onto the battlefield with The Gitrog's triggered ability doesn't count as playing a land
It would be too strong for Modern, and the only reason it doesnt see more play in Legacy is both Brainstorm and Ponder being legal alongside it (though it does show up some)
Your Treasure tokens are only good for one mana each, since you need to sacrifice them to get anything out of them