Missing the Timing: If “Dark Magician of Chaos” is Special Summoned in the middle of a chain (if it is not the last effect in the chain to resolve), the timing will not be correct for its Optional Trigger Effect, so you do NOT return a Spell Card from your Graveyard to your hand.
You can Special Summon “Dark Magician of Chaos” with “Monster Reborn”, and then return the “Monster Reborn” to your hand with “Dark Magician of Chaos”’ effect.
If you Special Summon “Dark Magician of Chaos” face-down with “The Shallow Grave”, its effect does not activate.
When “Dark Magician of Chaos” is Special Summoned with “Reasoning”, his effect activates.
When multiple “Dark Magicians of Chaos” are Special Summoned simultaneously, all of their effects activate; the controller starts putting their effects on a chain.
When you Tribute Summon “Dark Magician of Chaos” with “Sangan” or “Burning Algae”, those cards effects are Step 1 of the chain, and “Dark Magician of Chaos”’ effect is Step 2.
When you Special Summon “Dark Magician of Chaos” with “Last Turn”, you can activate “Dark Magician of Chaos”’ effect.
“Dark Magician of Chaos”’ effect targets 1 Spell Card in the Graveyard, so it will be negated by “Necrovalley” or “The End of Anubis”.
The Spell Card is chosen at activation of “Dark Magician of Chaos”’s effect, so your opponent could chain “Disappear” or “Graverobber” to deny you that Spell Card.
If “Dark Magician of Chaos” attacks a face-down “Fiber Jar” or “Cyber Jar”, the Jar is removed from play but its effect is activated.
If “Dark Magician of Chaos” attacks a monster with equal ATK, both monsters are removed from play.
When “Dark Magician of Chaos” is sent to your hand by “Penguin Soldier”, it is removed from play instead.
When “Fiber Jar” resolves, “Dark Magician of Chaos” is removed from play instead of returning to the Deck.
When “Dark Magician of Chaos” is removed from play by “Interdimensional Matter Transporter”, it is removed from play but will return to play as normal due to “Interdimensional Matter Transporter”’s effect.
When a face-down “Dark Magician of Chaos” is destroyed, it is NOT removed from play.
If “Dark Magician of Chaos” is equipped to “Relinquished”, and is destroyed, then “Dark Magician of Chaos” is removed from play. While “Dark Magician of Chaos” is equipped to “Relinquished”, you cannot select “Dark Magician of Chaos” as a card to send to the Graveyard for the effect of “Emergency Provisions”.
While “Skill Drain” is active, the first and second effects of “Dark Magician of Chaos” are negated, but the 3rd effect is not negated.
Netrep Rulings:
If “Dark Magician of Chaos” destroys a face-down Flip Effect monster in battle, the Flip Effect will resolve before that monster is removed from play.
“Dark Magician of Chaos’s” effect of retrieving a Spell Card from the Graveyard does not activate if “Dark Magician of Chaos” is Special Summoned face-down.
“Dark Magician of Chaos’s” effect of removing itself from play activates at any instant of “Dark Magician of Chaos” being removed from the field.