[2020] I don't remember Super Mario Bros. being this.....................creepy and dreary.

This is what happens when you don't wipe data during experimental like you're supposed to.

You are most likely playing an older save and a block might have been renamed/deleted or is on a server that has that issue. the block is an identifier to a missing block. (designed to do this)

if you see this in new map and not modded... then please let us know (by posting proper bug report in link given at top of page), which poi you found this in and if outside drop console and type DBS that will show us seed and location...

This has been reported several times already and each time a brand new map seed fixed it.. sorry but the old saying is still true... we are in alpha and things change.

You can identify the block in debug mode by looking at it and holding shift with the F3 debug info up.