From Sonic Retro
Matryoshka Bom is a badnik in Sonic Mania's Metallic Madness Zone. It isn't listed in any instruction manual, however it is referred to as "MatryoshkaBom" in the game's internal object list - the unusual spelling is almost certainly a reference to Sonic the Hedgehog CD's Bigbom badnik, which it appears almost identical to. Its behaviour, however, is very different: if the player gets too close, the badnik will open up and spit out a smaller version of itself before lighting its fuse. When the player is close, the smaller version will also open up and eject an even smaller version before lighting its own fuse. The smallest version functions almost identically to the Bomb badnik from the original Sonic the Hedgehog game, though with a much faster walking speed.