Random Block
In-game, the name is obfuscated (the glitchy changing letters thingy (§k))
When placed, it turns into one of 64 possible textures.
When broken, they all drop the same base Random Block, so you can't choose or pickup specific variants. They can be moved with pistons.
Recipe: 2 Infinitys and 2 Iron Nuggets in a checkerboard pattern.
Trivia
All of the textures were originally created with MCreator's built-in texture generator, but I deemed them dumb idiot stupids so I manually remade all of them and they're super pretty now.
Gallery
Placing Random Blocks
Every possible texture:
Sorry for the eye strain.