This card is unaffected by other card effects. Monsters you control gain 500 ATK, and are treated as DARK monsters, in addition to their normal Attribute. This card's controller may use their Spell & Trap Card Zone as an extra Monster Card Zones. Monster Cards summoned in the Spell & Trap Card Zone are still treated as Monster Cards, and can still declare an attack. However, they cannot be declared as an attack target unless their controller's Monster Card Zone is unoccupied.

According to wikia:

All monsters you control gain 500 ATK. This card cannot be destroyed or negated by card effects. Your Spell & Trap Card Zones are also treated as Monster Card Zones. Monsters in your Spell & Trap Card Zones cannot be selected as attack targets unless your original Monster Card Zones are unused. During your Main Phase, you can move monsters from your original Monster Card Zones to your unused Spell & Trap Card Zones, and vice-versa. When this card is activated, destroy all cards you control that list "The Eye of Timaeus", "The Claw of Hermos", or "The Fang of Critias" in their texts, and return any other cards listed in their card texts to the field.

AND

According to Konami, the anime effect text of "The Seal of Orichalcos" also included the following effects, consistent with the released TCG/OCG text:

• "Once per turn, this card cannot be destroyed by card effects." This is inconsistent with Gurimo's claim that the Seal was entirely indestructible by card effects, but it is impossible to verify, as in the anime, Yugi Muto only ever attempted to destroy the Seal once and never tried again. Konami states that Gurimo was lying about his claim.
  
• "You cannot Special Summon monsters from the Extra Deck." This is not consistent with the anime, as Rex Fusion Summoned "Horned Saurus" while he controlled the Seal (however, no one else did).
  
• "You can only activate "The Seal of Orichalcos" once per Duel." This was never said by anyone in the anime, but is consistent with its appearances and matches up with the fact that the loser of the Duel will be sealed within the card (requiring the winner to get a new copy if they wish to use it again).

---