You might not expect it to be the Dragon-focused colors, but it actually has a lot of great options with them: red and black
Card not found, on the other hand, is the basis for a deck in Modern (its namesake actually) and played in Legacy Storm decks (maybe Vintage as well, I dont know the format enough to say)
If another player gains control of Pietra, they can tell a joke you've already told, as long as they haven't told that joke yet
The natural inclusions in any deck playing Darcy are Mishras Bauble, Unholy Heath and, if paired with Blue, Expressive Iteration and Counterspells
Needless to say, he was not pleased and I'm pretty sure he didn't win the game
Any other replacement effect that would apply to the number of loyalty counters it enters the battlefield with will apply as normal