Fiend Deck

Dark Necrofear Deck
This build centers on the summoning of the monster Dark Necrofear, released in Labyrinth of Nightmare and reprinted in Dark Beginning 2. Boasting a pretty high 2200 ATK and a powerful 2800 DEF, this monster's special ability is what makes it special. Capable of stealing an opponent's monster when it's destroyed by equipping to the selected target as an Equip Spell Card (just like Snatch Steal but without the Life Point gain) makes Dark Necrofear very hard to get rid of. Most of these decks use Newdoria and Giant Germ to maintain field presence and gather Fiends in the Graveyard. Kuriboh can also be used to gather Fiends in the Graveyard to summon Necrofear and because of the summoning cost of this card (removing 3 Fiend-Type monsters in your Graveyard from play), many players use it in conjunction with Dimension Fusion and Return from the Different Dimension to summon every removed monster and attack for game.

Archfiend Deck
Those decks use the Archfiend monster family, released in Dark Crisis, and reprinted in Dark Revelation 1. Archfiends are fast monsters, with a lot of powerful Level 4 attackers like Archfiend Soldier and Shadowknight Archfiend. Terrorking Archfiend is a powerful monster with only 4 stars that is capable of negating the effects of any monster it destroys. It's only drawback is its summoning requirement (having an Archfiend monster card face-up on your side of the field in order to Normal Summon or Flip Summon this card). Archfiend monsters have 2 effects in common:
 * The first one, which states that you must pay a certain amount of Life Points to keep these monsters on the Field. This cost is not optional, and you must pay if possible. If you run out of Life Points, Archfiend monsters are destroyed immediately.

The Life Point cost is the main weakness of this deck.Pandemonium is a Field Spell Card that prevents both players of paying the Life Point cost (and allows to a player whose Archfiend monster is destroyed to search his/her deck for another Archfiend monster with a lower level than the destroyed one and add it to his/her hand). Because Archfiend Decks rely on Pandemonium to avoid losing due to its own costs, players tend to avoid this type of build.
 * The second one, that allows to the controller of an Archfiend monster card to roll a six-sided die when that monster is targeted by an effect. Each monster states a (number of) result(s), and if the die provides that result, the targeting effect is negated and the targeting card is destroyed.

Monsters

 * Raviel, Lord of Phantasms
 * Shadowknight Archfiend
 * Terrorking Archfiend
 * Skull Archfiend of Lightning
 * Archfiend General
 * Imprisoned Queen Archfiend
 * Pandemonium Watchbear
 * Inferno Hammer
 * Archfiend Soldier
 * Mist Archfiend
 * Dark Necrofear
 * Archfiend of Gilfer
 * Cyber Dragon
 * Darkbishop Archfiend
 * Sinister Serpent
 * Warrior of Zera
 * Mazera DeVille
 * Dark Ruler Ha Des
 * Kuriboh
 * Mad Archfiend
 * Dark Resonator
 * Dark Tinker
 * Evil Hero Infernal Gainer
 * Infernalqueen Archfiend
 * Legendary Fiend
 * Caius the Shadow Monarch
 * Prime Material Dragon

Spells

 * Checkmate
 * Dark Designator
 * Field Barrier
 * Falling Down
 * Heart of Clear Water
 * D.D. Designator
 * Hammer Shot
 * Pandemonium
 * Archfiend's Oath
 * Convulsion of Nature
 * The Puppet Magic of Dark Ruler
 * Axe of Despair
 * Gravekeeper's Servant
 * Reload
 * D.D.R. - Different Dimension Reincarnation

Traps

 * Sakuretsu Armor
 * Battle-Scarred
 * Curse of Anubis
 * Nightmare Wheel
 * Hate Buster
 * Final Attack Orders
 * Nightmare Archfiends
 * Prideful Roar
 * Solemn Wishes
 * Dark Illusion

Synchros

 * Red Dragon Archfiend
 * Thought Ruler Archfiend

Dark World Deck
This Deck type centers on the use of Dark World monsters, introduced in Elemental Energy, to dominate the field by using cards with discarding effects, like Morphing Jar, Card Destruction and Dark World Lightning, or by forcing the opponent to discard cards from the user's hand by effects like Dark Deal or Dragged Down into the Grave (a well-known combo is to give your opponent your face-down Morphing Jar with Creature Swap and then attacking it to trigger the Jar's effect and cause a discard "by your opponent's card effect", very bad news for the player not using Dark World). A Dark World build is fast, and can occupy the 5 monster card slots very quickly, but that causes a very small hand size. Card of Safe Return and Broww, Huntsman of Dark World are used to prevent that, as well as Morphing Jar. Another good Idea with this deck is to use Darknight Parshath. Since you are constantly discarding monster cards and most of the discarded monster cards are DARK type, Parshath will gain 100 ATK for each one. If you have Mystic Plasma Zone on the field it gives DARK monsters a 500 ATK boost and if you have at least 6 DARK monsters in the graveyard, Parshath becomes a single tribute 3000 plus ATK monster.

Monsters

 * Zure, Knight of Dark World
 * Renge, Gatekeeper of Dark World
 * Kahkki, Guerilla of Dark World
 * Gren, Tactician of Dark World
 * Scarr, Scout of Dark World
 * Beiige, Vanguard of Dark World
 * Broww, Huntsman of Dark World
 * Brron, Mad King of Dark World
 * Sillva, Warlord of Dark World
 * Goldd, Wu-Lord of Dark World
 * Reign-Beaux, Overlord of Dark World
 * Morphing Jar
 * Raviel, Lord of Phantasms
 * Great Maju Garzett
 * Goblin King
 * Doom Shaman
 * Dark Necrofear
 * Darknight Parshath
 * Dark Resonator
 * Dark Ruler Ha Des
 * Gorz the Emissary of Darkness
 * Legendary Fiend
 * Darkness Neosphere

Spells

 * Dark World Dealings
 * Gateway to Dark World
 * Dark World Grimoire
 * Dark World Lightning
 * Mystic Plasma Zone
 * Dark Designator
 * The Cheerful Coffin
 * Swords of Concealing Light
 * The Puppet Magic of Dark Ruler
 * Card Destruction

Traps

 * Dark Deal
 * The Forces of Darkness
 * Fine

Synchros

 * Stardust Dragon
 * Red Dragon Archfiend

Monsters

 * Raviel, Lord of Phantasms
 * Yubels
 * Sangan
 * Dark Crusader
 * Earthbound Immortal Ccapac Apu
 * Archfiend Soldier
 * Mystic Tomato
 * Giant Orc
 * Goblin King
 * Grinder Golem
 * Evil Hero Infernal Gainer
 * Mask of Darkness
 * Wall of Illusion
 * Doom Shaman
 * Familiar Knight
 * Dark Ruler Ha Des
 * Darkness Neosphere
 * Beiige, Vanguard of Dark World
 * Sillva, Warlord of Dark World
 * Zure, Knight of Dark World
 * Newdoria

Spells

 * Lightning Vortex
 * Tribute to the Doomed
 * Brain Control
 * Smashing Ground
 * Magical Mallet
 * Dragged Down into the Grave
 * Sword of Dark Destruction
 * Black Pendant
 * Inferno Tempest

Traps

 * Scrap-Iron Scarecrow
 * Cemetery Bomb
 * Hate Buster
 * Magic Cylinder
 * Trap Hole
 * Shadow Spell
 * Spellbinding Circle
 * Metalmorph
 * Trap Jammer
 * Return from the Different Dimension