Dranskar's Gate of Convergence

Technically this spell should be considered a 12th level spell. It is illegal everywhere without exception due to the steep price for the spell. A circle must be made from the blood of a Hydra with the specific symbol for a planar gate and a death transmutation. The spell can only be activated on a day of harmonic convergence when all the planets align and only if all components are within the center circle of the transmutation circle. Several extremely powerful spell casters are required to start the spell. Only one living creature can be inside of the center circle with the various components, any number of living creature can reside within the larger circle, and that circle has no limit to its size. 

At the start of the transmutation, all living humans and creatures who are not in the center circle are consumed. Their bodies are reduces to dust but their souls are not consumed. At the the very start, the lines of the circle will shine brighter than the sun. After enough humans have been consumed the light will expand and beam up to the convergence, shooting a line into the sky engulfing each planet.

A gate opens to each of the 23 planes. First merging the Feywild and Shadowfell with the the material plane. This is done without changing the landscape of the material plane. As the Elemental planes begin to merge, the already merged planes are mixed with each elemental plane drastically changing the landscape. As the 16 outer planes merge, the landscape becomes unrecognizable showing only faint traces of the material plane. All deities and creatures are also drawn from each plane.

Each deity is slowly drained of all power and left as mortals. Their power can be visibly seen emerging from their bodies and flowing like wind towards the center of the transmutation circle. Each component is reduced to dust. The power of each deity is infused with the living creature at the center circle. The merging of the planes effects the entire world and solar system outside of the circle as well as inside.

That person now has the strength of all the gods.