Rayman, a long running franchise, originally was gonna have a 4th game that was canned in favor of the Rabbids and their shenanigans in Rayman Ravin Rabbids for the Wii, which was a party game with the titular character. Since then, we've had more content with the Rabbids rather than the main man Rayman himself.
However, on early December 24 (Christmas eve), Rayman 4 which has long since been considered lost media was leaked at approximately around 6am. The entire source code and engine for the long-lost game was leaked alongside the very prototype itself.
Most of the game seems to follow the formula the 3D format Rayman games were already following, this time around, there appears to be a lot more to do.
From what's been observed, there's a mana system, rideable mounts, the "introduction" of sorts to the Rabbids and... Rayman's... Girlfriend?! These, alongside the Wizards that we see in Rayman Origins and onward.
Rayman 4 definitely looked like it was well into development before it got scrapped altogether.Source: GameRant via ResetEra