Once per turn, when an opponent's monster declares an attack: Target the attacking monster; destroy that target, and if you do, inflict damage to your opponent equal to half the destroyed monster's ATK. You must control an "Earthbound Immortal" monster with ATK higher than the ATK of the attacking monster to activate and to resolve this effect.
Those Majestic Synchros? In Speed Duel format with the cardpool we have right now?
Nobody use them even in real life, too much effort to summon a monster that lasts on the field for just 1 turn no matter what. Not to mention needing a deck specifically for them since the Tuner can only be used for them.