Most Duelists pack their Decks with monsters that have the strongest effects they can find. Fiendish Chain can negate those monsters’ effects and render those monsters unable to attack. If you shackle your opponents’ monsters with Fiendish Chain, your opponent will be forced to rely on other monsters to win.

Some of the strongest monsters in the game also have the best effects. Judgment Dragon has 3000 ATK, Dark Armed Dragon has 2800 ATK, Gladiator Beast Gyzarus has 2400 ATK, and all of these monsters can destroy cards on the field. Fiendish Chain takes away all of their strengths at once.

Make these monsters useless by activating Fiendish Chain!
Unlike Skill Drain and Forbidden Chalice, which can also negate the effects of your opponent’s monsters, Fiendish Chain will protect you from those monsters’ attacks too! Fiendish Chain also has some other advantages over these two cards.
Skill Drain has the drawback of negating all of your own monsters’ effects. The effects of Fiendish Chain, on the other hand, can be controlled more easily. You get to choose the monster you want to see affected by Fiendish Chain, and your monsters will keep all of their effects.
Forbidden Chalice has the drawback of only lasting until the End Phase, while Fiendish Chain paralyzes your opponent’s monster for as long as it remains on the field. When you use Forbidden Chalice on an opponent’s monsters, that monster will also gain an additional 400 ATK to attack you with.
Fiendish Chain is especially good against Decks that rely on certain monster effects to turn the Duel around. Since Fiendish Chain can make the effects of Dark Armed Dragon, Judgment Dragon, Chaos Sorcerer, and Phantom of Chaos inaccessible to your opponent, it can be a strong Side Deck option to use against Twilight Decks. Fiendish Chain can also be used to negate the effects of any of your opponents’ Monarch Tribute Monsters, including Caius the Shadow Monarch and Raiza the Storm Monarch. This makes it a useful card to Side Deck in against Monarch Decks too.
Since Fiendish Chain can also be used to negate the effects of strong Synchro Monsters like Brionac, Dragon of the Ice Barrier and Mist Wurm, it can be a useful card against just about any Deck.
But watch out for monsters whose effects activate in the Graveyard! Fiendish Chain negates monsters’ effects while they’re on the field with Fiendish Chain, but doesn’t negate effects that take place while the monster is off the field. It also doesn’t stop opponents from activating their monsters’ effects. This means that your opponent can still activate the effect of Stardust Dragon or Exiled Force, even if you chose to negate its effect with Fiendish Chain. Monsters like Mystic Tomato and XX-Saber Emmersblade also can’t have their effects negated by Fiendish Chain, since they activate in the Graveyard.
Fiendish Chain has a lot of uses and can sometimes get you out of a tight spot. The power to tie up one of your opponent’s monsters so it can’t attack and loses its effect is unique to Fiendish Chain and can be especially strong against certain Duelists. Try it out and see how often it comes in handy.