Ghost levels are a go
Mutant Mudds was released on the Nintendo 3DS all the way back in 2012, but it's still updated to this day. In addition to adding the Granny levels that were introduced with the PC version of the game, developer Renegade Kid has just added the special ghost levels that were present in the Wii U Deluxe edition.
It is very rare for developers to do this in terms of feature parity between versions. Most of them just leave the appropriate consoles to their own devices, so good on Renegade Kid to give back to their fans. As a side note, since the PAL region never got the Wii U edition of the game due to problems with Nintendo of Europe, this is their first chance to play the ghost levels (they're good).