This card’s effect includes itself, as long as it remains a Fiend-Type monster.
Flip Effects and effects that activate in the Graveyard WILL be negated. This includes
"Sinister Serpent",
"Sangan",
"Witch of the Black Forest",
"Marie the Fallen One",
"Mystic Tomato",
"Giant Rat",
"Masked Dragon",
"Magician of Faith",
"Man-Eater Bug",
"Nimble Momonga",
"Twin-Headed Behemoth", etc.
Monster effects that activate after damage calculation will be negated if your Fiend-Type monster destroys the opposing Effect Monster. Examples include
"D.D. Warrior Lady",
"Thousand Needles",
"Slate Warrior",
"Ryu Kokki", and
"Wall of Illusion".
If an Effect Monster, destroyed by a Fiend-Type monster while
"Dark Ruler Ha Des" is on the field, is returned from the Graveyard to the hand or Special Summoned from the Graveyard, its effect will be active again. Its effect may be negated again if destroyed by
"Dark Ruler Ha Des" or another Fiend-Type monster.
If one of these Effect Monsters is removed from play (by
"Soul Release" for example) and then returned to the Graveyard with
"Miracle Dig", the negation condition was lost and the effects will now be active.
If
"Kisetai" is attacked by a Fiend-Type monster while
"Dark Ruler Ha Des" is on the field, its effect prevents damage calculation, so it is not destroyed and its effect is NOT negated.
If
"Sinister Serpent",
"Twin-Headed Behemoth", or
"Marie the Fallen One" is destroyed by a Fiend-Type monster when this card is on the field, they will not activate on any following turn. So during your opponent’s next Standby Phase, and each of his/her following Standby Phases, they may NOT move
"Sinister Serpent" to their hand, Special Summon
"Twin-Headed Behemoth", and they will NOT gain Life Points by the effect of
"Marie the Fallen One". This negation continues even if
"Dark Ruler Ha Des" is later removed from the field.
If your Fiend-Type monster battles with
"Relinquished" equipped with a
"Sangan" or a
"Witch of the Black Forest" and the equipped card is destroyed instead of
"Relinquished", the effect of
"Sangan", etc., will activate since it was the effect of
"Relinquished" that destroyed it. It was not destroyed as a result of battle with the Fiend-Type monster.
If your
"Dark Ruler Ha Des" or other Fiend-Type monster destroys
"Tyrant Dragon" as a result of battle, a Dragon-Type monster must still be Tributed when
"Tyrant Dragon" is Special Summoned from the Graveyard. This is because Tributing a Dragon-Type monster is a condition on the Summoning of the card; it is not part of the effect. For the same reason, if a Spirit Monster is destroyed by a Fiend-Type monster when
"Dark Ruler Ha Des" is on the field, it still cannot be Special Summoned from the Graveyard. Also if two
"Dark Ruler Ha Des" destroy each other in battle, neither can be Special Summoned from the Graveyard.
"Dark Ruler Ha Des" cannot be Special Summoned from the Graveyard even if you try to Special Summon it face-down by the effect of
"Spear Cretin" or
"The Shallow Grave".
You can activate
"Return of the Doomed" to return
"Dark Ruler Ha Des" to your hand during the turn which it was destroyed, because this does not Special Summon it, it merely returns the card to your hand.
The effect of
"Fiber Jar" will shuffle
"Dark Ruler Ha Des" back into your Deck even if
"Dark Ruler Ha Des" is in the Graveyard and cannot be Special Summoned.
"Dark Ruler Ha Des" may be Special Summoned by
"Dimension Fusion" or
"Return from the Different Dimension" if it was removed from play.