The Bigbom seems to be a giant version of the Bomb that first appeared in Sonic the Hedgehog (1991). They have large red and grey round body with red and blue buttons and a face plate with blue button that looks like its eye. On top of its head is a fuse that ignites once it sees its target. The Badnik is able to walk back and forth with pair of mechanic legs.
Sonic the Hedgehog CD
The Bigboms appear exclusively in Metallic Madness. They are placed on paths near tight corners or in wide hall sections, where the player can move behind the setting. Bigboms usually walk back and forth, but when one of them notices Sonic, it runs towards him while staring its self-destruction countdown. Like Bombs, Bigboms release six sparkling projectiles into the air when they explode. As the player has to advance through the Zone, kinky placements of Bigboms make it impossible to avoid them and dodging their projectiles can be tricky. Like Bombs, the player can also not destroy them.
Bigbom is notably the only Badnik in the game that does not have a broken form due to age. It is also one of the few Badniks that does not release Little Planet flower seeds.
In gameplay, they behave similarly to how they acted in Sonic the Hedgehog CD. In this game however, they act like a "Matryoshka Doll": upon encountering one, a Bigbom will open its mouth and drop a medium Bigbom and then it will drop a smaller Bigbom.
↑While not listed in any instruction manuals, the in-game source code in 1996 PC release of Sonic the Hedgehog CD refers to this Badnik as "bigbom".