Door of death

Door of death was a spell that could only be cast by dragons.

Effects
A dragon cast this spell onto a portal, whether a door or the entrance to a cave. The portal had to have a diameter less than. Only the portal itself was warded, the surrounding wall was not. Once cast, any creature crossing the portal without uttering the proper command word became the victim of a death spell. During casting, the dragon could choose whether the spell was to radiate an aura of necromantic magic. This blue aura was visible in low-light and surrounded the perimeter of the portal.

Casting
This spell required only a verbal component.