Most of the Prismrivers' solo cards fall under this in general, I think. Lunasa's Stradivarius on Hard is probably a lot worse than Pseudo Stradivarius on Lunatic.
There's also Murasa's timeout spell. Sinker Ghost is a lot harder than Dipper Creeping Close.
The biggest example, though, is almost certainly Archimedes' Pump, the second card from the second boss in Marine Benefit Hard. It's not just harder than the Lunatic version, it's probably the hardest card in the entire game on that difficulty, and comparable to many of the harder Lunatic spells.
Also from MB, there's Megumi's second boss card, where the difficulty is seriously borked. The Easy version is harder than the Normal version, which in turn is harder than the Hard version.