Blast Magician (SD6-EN014) [Structure Deck: Spellcaster's Judgment]

Each time you or your opponent activates 1 Spell Card, put 1 Spell Counter on this card. By removing any number of Spell Counters from this card, destroy 1 face-up monster on the field with an ATK equal to or less than 700 points x the number of removed Spell Counters.