I got a great auto-duel deck for the level 51 duelists. Won 10 in a row with auto-duel (sometimes you might have to step in though).
skill: Balance
Kaiser Sea Horse x 1
Rigorous Reaver x 1
Sphere Kuribo x 1
Grasschopper x 1
Leotaur x 2
Blue Eyes White Dragon x 1
Dunames Dark Witch x 1
Jerry Beans Man x 2
Riryoku x 2
Black Pendant x 1
Gravity Axe x 2
Mirror Wall x 2
Michizure x 2
Magic Jammer x 1
Of course you can improve this squad by putting in more Dunames Dark Witches and Jerry Beans Man instead of Blue Eyes White Dragon, Rigorous Reaver, Kaiser Sea Horse
After 50+ autoduels, I can still say this is a good deck, but every once in a while it struggles with the spirit monsters, still 90-95% auto-win ratio though.
Would definitely recommend 3 Mirror Walls if you have 3, and lose one Michizure.
Thanks PK, It seems to be working, just won my last 6. I had to replace the cards I don't have. I replaced 1x Mirror wall by windstorm of Etaqua, 1x Leotaur by Bazoo the Soul-Eater , Dunames Dark Witch by Twin Barrel Dragon, Jerry Bean Man by Cocoon of Evolution and finally BEWD(because I am not a big fan :D ) by The Fiend Megacyber and Millennium Scorpion
Yeah not long after I posted that team I replaced BEWD as well with The Fiend Megacyber, now by Summoned Skull. If you can't get Mirror Wall, get the new trap card Rising Energy, it's like a more versatile version of Mirror Wall that instead of halving your opponent's attack, adds 1500 to your attacking power which can you use in defence and attack.
This is the best deck I've seen for this stage. I've wasted so much time and so many keys on decks posted in comments on this site, but this paid off. I'm using a modified version since I'm short the UR traps, but I'm still pulling 90%+.
PK
PK
