TCG Rulings
- If the monster battling "Mythical Beast Cerberus" is removed from the field before (or during) Damage Calculation, the Spell Counters on "Cerberus" will not be removed.[1]
- Removing the Spell Counters from "Mythical Beast Cerberus" does not start a chain.[1]
- The Spell Counters on "Mythical Beast Cerberus" are removed after he battles no matter which player is attacking.[1]
OCG Rulings
- Removing the Spell Counters from "Mythical Beast Cerberus" after it battles does not start a Chain.[2]
- The effect "Once per turn, if you remove a Spell Counter(s) from your side of the field to activate the effect of a card effect you control, you can remove the Spell Counters(s) from this card instead." of "Magical Citadel of Endymion" can only be used for costs. It cannot be used when an effect like "Mythical Beast Cerberus" removes Spell Counters.[3]