What is the Destroyer Shout on the menu for alliance buildings?

Destroyer shout takes 5 min to cast & it clears an area 5x5 of tiles. Once the cast is started everyone in the state can attack the castle that is casting it & that is why the strongest member of the alliance should cast it & must be reinforced by other very strong members. If the cast is successful you can place a Rally Point on the area cleared by the destroyer & have also space for castles to teleport near the Rally Point. If the cast fails (the caster castle is zeroed or shouted away by dragons) then the destroyer dragon is consumed & the cast must start again.