Fiend Deck

This type of deck is based on Fiend-Type monsters. With a lot of powerful attackers and a variety of weak monsters with nice effects, Fiends are a force to be reckoned with. Since most of Fiends with a high ATK score are Dark monsters, they usually do very good combos with Deck Devastation Virus. There are 3 main types of Fiend Decks: Dark Necrofear decks, Archfiend decks and Dark World decks.

Decks based in Dark Necrofear
This build centers on the summoning of the monster Dark Necrofear. Boasting a powerful 2200 ATK and a pretty high 2800 DEF, this monster's special ability is what makes it special. Capable of stealing an opponent's monster when it's destroyed as result of battle or by your opponent's card effect 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 this decks use Newdoria and Giant Germ to mantain field presence and gather Fiends on the Graveyard. 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. Decks that use this pair of cards as its win condition are called "Necrofear Return" decks.

Archfiend Decks
Those decks use the Archfiend monster family, released in DCR and reprinted in DR1. 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 of 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 this 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 inmediately.=

=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.=

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.

Dark World Decks
This Deck type centers on the use of Dark World monsters 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 the Safe Return and Broww, Huntsman of Dark World are used to prevent that, as well as Morphing Jar.