When you take a Magic action to read this scroll, a Tarrasque appears in an unoccupied space on the ground or in water that you can see within 1 mile of yourself.
The Tarrasque is Hostile toward all other creatures and disappears when it drops to 0 Hit Points. If the Tarrasque is summoned into a space that isn't large enough to contain it, the summoning fails, and the scroll is wasted.