Mana produced by Creeping Peeper's activated ability can be used to pay morph or disguise costs when turning a face-down permanent face up or to pay costs associated with turning a manifested or cloaked permanent face up
After all, not everyone has almost $1000 laying around just to spend on a single card, even if it is exceptional
8 Animal Sanctuary There's finally a reason to cram all the best Dogs, Cats, Goats, Oxes, Birds, and Snake creature cards into one deck: Animal Sanctuary
Urborg, Tomb of Yawgmoth + Yavimaya, Cradle of Growth Urborg, Tomb of Yawgmoth and Yavimaya, Cradle of Growth occupy a similar space of making all lands duals of a sort
Many Avatar: The Last Airbender cards pay you off for having lesson cards in your graveyard like Iroh, Grand Lotus or Ran and Shaw
They spend a good chunk of the game catching frogs in Qu's Marsh (there's even a golden frog sidequest), while their main battle ability is actually "Eat" - consuming weakened enemies to learn Blue Magic (enemy skills)