In the actual (original, despite appearances to the contrary) English episodes, the name of the two-headed snake Grimm is spelled and pronounced "King Taijitu" without the s. Changing tag and wiki page.
bunkhead said: The snake isn't called Ouroboros? What a waste of opportunity.
The Ouroboros is a snake that coils around to bite its own tail, symbolizing an endless loop. If they wanted to name it directly after a mythological creature, they could have chosen the Amphisbaena instead, which can be depicted as a snake with a head at each end. The chosen name has its own meanings: the "King" may be an allusion to King Ghidorah, a multi-headed enemy of Godzilla and sometimes-enemy-sometimes-ally of Mothra; and (more significantly) the "Taijitu" is the proper name of the yin yang symbol, represented on the snake's body as the center portion where the black and white scales intermingle with each other and with gray scales.