The Underworld Tree is where all universes collide. The Tree itself is a large, upside-down sweetgum tree located somewhere outside a galaxy. The location changes based on universe. Can be considered the center of the universe.
There are many ways to destroy the universe or kill a galaxy-deity. The easiest of these would be to locate two Peasant-trees and deprive them of oxygen. This will kill that universe's branch of the Underworld Tree. The next easiest would be to find the Universal Reset Button, out floating in empty space, at the furthest point from any galaxy. Star-carvers guard the Button, which looks just like a normal red button. When pressed, the Universal Reset Button sends the current universe back to 0.0000000001/2^-pi seconds after the Big Bang, essentially restarting the universe. The final and most challenging would be to deal significant damage to the Underworld Tree itself, which will go into healing mode. If damaged again, the tree will die, ending all universes. Shards of Underworld Tree bark can be smelted like metal by the most talented metallurgists or blacksmiths into weapons. These weapons can kill even a galaxy-deity by unravelling them molecularly until they become a miniature nebula of the smallest of elements. The only known weapons in existence are the Stick of Lies, the Underworld Sword, and the Underworld Staff.
Most units of measurment use the Galactic Standard, which is a base 10 system.
Time is converted from planetary times by counting its rotations around the galaxy's center. This can cause a slight variance in time depending on how close a planet is to the center of its galaxy or how large a galaxy is.
For convenience, Galactic Standard is almost the same as the Metric system. We are all happy with this information.
A year in Galactic Standard, as well as in the Stardom, is 100 days.
Peasant-trees are trees that "work" for the Underworld Tree, in a sense. They exist in different universes, all over the place, and collect both nutrients and information for the Underworld Tree. Depriving one of oxygen would entail putting it in a depressurization chamber. Cutting it down isn't enough, as it will be able to come back from that.
Star-Carvers are a species of galaxy-deity. More about them here. *coming soon*
Metallurgists are similar to blacksmiths, but with the magical ability to shape metal.
The Stick Of Lies, the Underworld Swrod, and the Underworld Staff are three weapons given to the guardians of the Underworld Tree. They have enough stored energy to vaporize a mortal immediatly, and severly wound an immortal or galaxy-deity. The weapons falling into the wrong hands would be incredibly dangerous to the entire Tree system.
Being "Gifted" is a rare occurence, blessing a creature with physical or magical differences at birth. Having a Gift is more common hereditarily, but they can manifest on their own. Gifts are most common in Starcats. The Starcat Rebellion is made up of experimented-on cats who gained the first Gifts, and their descendants carried them on.