Dark Synchro Monster

Dark Synchro Monsters are a new monster category that debuted in Yu-Gi-Oh! 5D's episode 27. Dark Synchro Monsters are Synchro Summoned by sending to the Graveyard 1 Dark Tuner monster and 1 non-Dark Tuner monster. Besides the "Dark Tuner Monster", you can use any monster for the Dark Synchro Summon. The non-Dark Tuner Monster's Level minus the Dark Tuner Monster's Level must be equal to the Dark Synchro Monster's Level (note that the Dark Synchro Monsters have a negative level, something that isn't possible with any other monster in the game). Also, their levels start at the opposite side of the card (real cards start at the right side, they start at the left side).

Dark Synchro Monsters and Dark Tuner monsters are not simply DARK Synchro Monsters, but are a completely different monster category, although they are admittedly similar to Synchro Monsters. The color scheme of that is opposite of a Synchro Monster, with a black card frame.

It was shown that Dark Synchro monsters function as Synchro Monsters with Negative Levels for any game-related purposes when Yusei's Synchro Destructor dealt damage twice instead of just once because he destroyed Kiryu's One-Hundred Eye Dragon with his Stardust Dragon.

The only known Dark Synchro monsters are "Freezing Fitzgerald", "Jet-Black Zumwald", "One-Hundred Eye Dragon", and "Underground Arachne".

Example
Another Dark Synchro has been released in the anime, but it's name is not known. It is an ape, though.