During your opponent's turn, when your opponent activates a Spell Card (Quick Effect): You can Tribute this card; negate the activation, and if you do, destroy it.
Rulings
Individual Card FAQs
This monster's effect is Multi-Trigger, and therefore Spell Speed 2. So it may be used against Quick-Play Spell Cards.
Netrep Rulings
"Maryokutai" may be Tributed during the Damage Step as long as it is not involved in that battle.
WATER|
Level 3|[ Aqua / Effect ]
ATK 900|
DEF 900