Lana Valkyrie
Hakuro de Killer
But yeah, the Dark Synchros, though not like the Dark synchros from the series, could still have the potential to be overpowered. Especially in the current format which is mostly ruled by Dark Armed Dragon.
... Dark Armed Dragon hadn't ruled the format since March. That role has been taken by Dark Strike Fighter. Keep up with the times.
Nonetheless the changes dealt to One-Hundred Eyes Dragon, which has been seen by those who watch the series as one of the best if not the best Dark Synchro Monster, have been thusly poor. Specific summoning requirements and limited use of its effect by narrowing what it can copy in the Graveyard? Crap, and I don't expect anything to be much better as they continue to be translated.
Synchros are better. The translation of Dark Synchros are nothing compared to what we have now.
With all due respect, all Dark Armed Dragon did in march was get pushed down the ladder just a little bit. It ruled the format just a little, knowing the september banlist would get rid of the Dark Strike Fighter.
On a side note, One-Hundred Eyes Dragon will not see play as a staple card ever. Now, in certain decks (Such as Dark World or Infernity), I can see this card seeing a bit of play. Admittedly, using One-Hundred Eyes Dragon to remove a Jinzo and then, when it's destroyed, use Return from the Dark Dimension on said Jinzo might be a clever combo.
But I do agree that there are better synchros out there. However, most of the good synchros in the game are banned or down to 1 (Goyo, Black Rose, Dark Strike Fighter) and it has the potential to work in the right deck.
However, if you saw the episode where One-Hundred Eyes Dragon made an appearance (I saw the sub, not the dub, so I'm not sure if 4Kids carried over the misunderstanding), but it was implied in the show that, when One-Hundred Eyes Dragon is destroyed, you search for ANY 1 card in your deck and add it to your hand. It was not said that it had to be an Earthbound Immortal. That could be a potential reason for the misunderstanding.
Also, there are some Dark Synchros that can completely wreck face if they're allowed to work. A valid example of this would be Underground Arachne, which is a freaking beast that just might get limited. Other notable entries which may or may not be released are Frozen Fitzgerald and Moonlight Dragon Quilla alongside Sun Dragon Inti. Those are the only very good Dark Synchros in my opinion, but that's just me.