Why I chose Archfiend to be the deck of the month?
Many reasons to that, first archfiend is the oldest archetype in Yu-Gi-Oh and we can feel some nostalgia by using them.
The main reason is Archfiend receive a lot of great support and are able to become really competitive.
With some meta decks hit by the September ban list, Archfiend decks have a chance to become tier 2.
Well, let's see the new Archfiend cards :




Archfiend Heiress : Awesome searcher in this deck, works well with foolish burial, and can be special summon by tour guide.
This card can also search Archfiend's magic and trap cards.



Archfiend Cavalry : Great attack, and his effect allows you to reborn any Archfiend monster, but it can't attack the same turn.



Archfiend Commander : This card works well with Archfiend Heiress and Archfiend Cavalry because their effects activate when destroyed by Commander.
Use him to make some XYZ lv 6.




Archfiend Emperor, the First Lord of Horror : Not only is he badass, but he also has a really good effect. He can be normal summoned and immediately destroy one card on the field. When he is in the graveyard, he can be special summon by Cavalrys' effect.



Archfiend Palabyrinth : A great field for the new card, a good attack boost and helps to make more XYZ monsters. Can be search by Archfiend Heiress.

Of course there are many cards that work well with this archetype :

Monsters :

-Tour Guide, Xyz rank 3 with Heiress.
-Rescue Rabbit : Xyz rank 4 (Run it with 3 Archfiend Soldier),
-Masked Chameleon : Synchro 7 or 8 with Heiress and Cavalry.
-Armageddon Knight : Send Heiress or Emperor fast in grave from the deck.
-Dark Grepher : Special summon him for Xyz lv 4 + can send a card to the grave.
-Dark Armed Dragon : Easy to summon in this deck, awesome effect
-Dark Necrophear : Same as Dark Armed Dragon.
-Tragoedia : Great effect and fiend monster.

Spells :
-Allure Of Darkness : Lot of Dark monsters.
-Foolish Burial : Combo with Heiress.
-Falling Down : Awesome card that work with Archiend Palabyrinth too.
-Creature Swap : Use it with Heiress or Emperor on your field.
-Pandemonium : This old spell field still work well with the new cards.

Traps :
-Archfiend's Roar : Awesome card with Heiress and Cavalry. Searched by Heiress.
-Skill Drain : Great card in this deck, if you don't main it, side it !
-Hate Buster : Great card that allow you to get the effect of Cavalry too.

So here is an exemple of a complete deck (september list format) :

Monsters (20):
3x Archfiend Soldier
3x Archfiend Cavalry
2x Archfiend Commander
2x Archfiend Emperor
3x Archfiend Heiress
1x Dark Armed Dragon
1x Dark Necrophear
2x Masked Chameleon
1x Rescue Rabbit
2x Tour guide form the Underworld

Spells (12):
1x Allure Of Darkness
2x Archfiend Palabyrinth
1x Dark Hole
2x Falling Down
1x Foolish Burial
3x Mystical Space Typhoon
2x Pot Of Duality

Traps (8.):
2x Archfiend's Roar
1x Bottomless Trap Hole
1x Compulsory Evacuation Device
2x Hate Buster
1x Solemn Warning
1x Torrential Tribute

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Dark World Archfiend :

Monsters (18) :
3x Cavalry
2x Archfiend Emperor
3x Archfiend Heiress
2x Broww, Huntsman Of DW
2x Grapha, Dragon Lord Of DW
2x Snoww, Unlight Of DW
2x Tour Guide From The Underworld
2x Trance Archfiend

Spells (14) :
1x Allure Of Darkness
1x Dark Hole
3x DW Dealings
1x Foolish Burial
2x MST
2x Pot Of Duality
2x The Gates Of DW
2x Trade-In

Traps {8} :
2x Archfiend's Roar
1x Bottomless Trap Hole
1x Compulsory Evacuation Device
1x Eradicator Epidemic Virus
1x Return From A DD
1x Solemn Warning
1x Torrential Tribute

Have fun with them !