TCG Rulings

• This effect is a Quick Effect that must be chained directly to the card or effect that is targeting "Arcana Knight Joker".^[1]

• This effect does not target.^[1]

• Discarding a card is a cost to activate the effect.^[1]

• You cannot discard a card to negate the effects of "Premature Burial" or "Call of the Haunted" that destroy "Arcana Knight Joker" when they are destroyed.^[1]

• You can activate this effect during the Damage Step.^[1]

OCG Rulings

• The effect of "Arcana Knight Joker" which negates a Spell Card, a Trap Card, or the effect of an Effect Monster is a Quick Effect.^[2]

• The effect of "Arcana Knight Joker" is activated in Chain to the activation of the Spell or Trap Card.^[2]

• Discarding one Monster, Spell, or Trap Card is a cost to activate the effect of "Arcana Knight Joker".^[2]

Mentions in Other Rulings

• When Fusion Summoning a monster like "Dark Balter the Terrible" or "Cyber End Dragon" or "Destiny End Dragoon", you must use the Fusion Material Monsters that are specifically listed on the card. You cannot use a Fusion Substitute Monster like "Goddess with the Third Eye" or "King of the Swamp" as a Fusion Material Monster.^[3]

References

1. ↑ ^{1.0 1.1 1.2 1.3 1.4} Shriek TCG: Ancient Prophecy - Rulings
2. ↑ ^{2.0 2.1 2.2} Konami FAQ: Fusion Monster > Arcana Knight Joker
3. ↑ Konami FAQ: When Fusion Summoning a monster like "Dark Balter the Terrible", can you use a monster like "Goddess with the Third Eye" as a Fusion Substitute Monster?