The Underground Monsters, or Diggers, are a group of humans that were experimented on by Shredder's Foot Technicians, and turned into monsters capable of surviving deep underground. They appear in the 2003 TV series and 2003 video game. At least seven are known and four have official names: Quarry, Stonebiter, King Nail, and Razorfist. The other three are a Underground Spider Monster, Underground Insectoid Monster, and Underground Cyclops Monster. The effects of the Crystal Moon found in the Underground City can revert them back into humans.
The Foot Clan captured a number of innocent people and subjected them to horrendous experiments, transforming them into monsters capable of surviving underground. The Foot used these creatures to search the underground beneath New York for the Utroms, discovering an Y'Lyntian settlement in the process. Once it was determined that the Utroms were not hiding underground, the Diggers were ordered to be terminated. However, some of the Diggers retained their humanity and rebelled against the Foot, who then abandoned their underground outpost. Others were not so fortunate, prowling the tunnels, becoming nothing but mindless beasts.
When Michaelangelo incidentally caused two Y'Lyntian crystals to touch, a sound reached into the underground. The Diggers feared the crystals and went looking for the source. After some misunderstanding with the TMNT, the Diggers cooperated with the Turtles to find another crystal to maintain their force field, going deep down into the catacombs where they found the Y'Lyntian city. Pursued by the other monsters, each of the Diggers were soon transported into stasis chambers by the Entity, the city's sole Y'Lyntian guardian, where the crystal moon that powered the crystals could restore them to human form. Though he claimed he wanted the Diggers' aid in repopulating the city, it is presumed he intended them to be the slaves of a new Y'Lyntian empire.
After the Turtles imprison the Entity, they find the Diggers have reverted to human form. Unfortunately, they soon discover that straying too far from the crystal moon causes them to revert into their monster forms, forcing them to stay in the city. As the Turtles promise to return, the Diggers began to exhaust themselves trying to find a permanent cure.
After using up a lot of crystals, they tried using explosives to break a few chunks from the crystal moon. Unfortunately, they accidentally dislodged the crystal moon from the cavern roof, causing it to fall into the lava. Without its regenerative effects, the Diggers reverted to their monster forms, attacking anything that moved. When the Turtles returned with a cure, the Diggers attacked them. Donatello first administered the cure to Quarry, who reverted to her human form, Sydney. But to use more crystals to inoculate the others, they needed to restore the crystal moon. After raising the crystal moon from the lava, the Diggers became human again and were given the cure, enabling them to return to the surface.
Known Underground Monsters
- Quarry - An unspecified monster created from a woman named Sydney.
- Razorfist - A humanoid scorpion-like monster created from a red-haired man.
- Stonebiter - A humanoid rock monster created from an African-American man.
- King Nail - A mindless scorpion-like monster created from an unnamed man.
- Underground Cyclops Monster - A mindless rock-skinned cyclops-like monster created from an unnamed man.
- Underground Insectoid Monster - A mindless insectoid monster created from an unnamed woman.
- Underground Spider Monster - A mindless four-legged spider-like monster created from an unnamed woman.