Crock is is an enemy Badnik encountered in Rusty Ruin Zone, the second level of Sonic 3D: Flickies' Island.
Resembling a robotic alligator, the Badnik simply wanders back and forth along a straight line. It can only harm Sonic by bumping directly into him; destroy it with a Spin Dash or jump to recover its organic battery power source, a green Flicky, and make Flickies' Island a slightly less dangerous place.
The name of this Badnik is conjectural, as no official name has been given to it. The name comes from the level editor in a development build of Sonic 3D that is included as a bonus feature in Sonic 3D: Director's Cut. Jon Burton has confirmed that the name was used in the original game.