Dark Ones

Over millions of years, a race of red-skinned frogs somehow came to live in the Martian desert and evolved into the Desert Muck Leech (Cyprinodon martius). Since they tried to kill every species in existence, the Legion of Mad Fellows calls them the Dark Ones.

Endowed with mind-reading abilities, they tried to stop the Legion from reaching its goal of the Encyclopods' return. As a species, though, they were unsuccesful, as by 3009 only about 7 remained, all living in one scum puddle (now a gigantic parking lot in the new Mars Vegas).

Leo Wong killed them all except one, which was saved by Leela. The leech lived off Leela after several (unsucessful) eating attemts by Zoidberg.

It killed Frida Waterfall after it found out Fry was going to prevent the explosion of the Violet Dwarf. At the explosion ceremony, it was killed by an Encyclopod and eaten by Zoidberg after being crippled by the Omega Device.

Additional Info

 * "'Dark One:"' Go on, blow up the Violet Dwarf!
 * Leo Wong: You got it, Mr Voice In My Head!