The Wand of Watoomb is a magical wand with a demons head carved into one end.
Baron Mordo learned that the Wand of Watoomb was at the Sanctum Sanctorum and he sent his minions to the Sanctum to steal it. Mordo wanted the Wand of Watoom so that he could use it to open a portal to the Dark Dimension and bring Dormammu to Earth.
In another attempt to steal the Wand of Watoomb, Baron Mordo brainwashed Peter Parker and sent him to the Sanctum Sanctorum along with other cultist. This time they managed to obtain the Wand of Watoomb and gave it to Baron Mordo.
At the Center for Reunification, Baron Mordo used the Wand of Watoomb to open a portal to the Dark Dimension and was about to bring Dormammu to Earth. However, Doctor Strange, Spider-Man, and Wong arrived and Strange fought Mordo. Wanting to help Spider-Man jumpped through the portal with the Wand of Watoomb. However, Spider-Man was confronted by Dormammu. Doctor Strange then arrived to help Spider-Man. As Dormammu ordered Spider-Man to give him the Wand of Watoomb, Spider-Man threw the wand into the air and Dormammu chased after it. However, Spider-Man caught the Wad of Watoomb with a web line. Doctor Strange and Spider-Man then went through the portal back to Earth and Doctor Strange used the Wand of Watoomb to close the portal to the Dark Dimension.
Doctor Strange then took the Wand of Watoomb back to the Sanctum Sanctorum.
The full extant of the Wand of Watoomb's power is unknown.
Baron Mordo used the Wand of Watoomb to open a portal to another dimension.
In the comics
The Wicked Wands of Watoomb are six mystical artifacts from varying dimensions which were all built by the mystical being, Watoomb. They are one-foot long crystalline batons with demonic heads carved on wither end.
Objects of near-omnipotent power, each Wand is controlled by mere thought of it's user, primarily for enhancing, multiplying, gathering, focusing, and redirecting mystical energies. They can be used to block mystical attacks, and use the energy absorbed to either heal the wielder, unleash a damaging blast, or erect a defensive barrier. They can also be used to control the elements, open portals to other dimensions, and allow the wielder to show the future of any person, place, or thing they are familiar with.
The first revealed Wand of Watoomb had been broken in half, but followers of Dormammu had it restored. It was later seized by Doctor Strange.