While everyone knows about the various planes and some have visited these like the Mortal Plane, Fire Plane, or the Nine Hells. Who can say they travel to various other worlds that have their own versions of the Mortal Plane and the Fire Plane? With the ability of World Shift, the most skillful and powerful of spellcasters can take a chance to travel from their world to another, say from the Forgotten Realms to Exandria, then to Eberron, the number of worlds could seem endless than the Planes you once knew. 

The way you travel the worlds through this spell can depend of the spell caster's preferences, like summoning a mirror like object to travel through or tree striding through the worlds. You and up to eight willing creatures are allowed to traverse this doorway to another world but their hands must be link to the spellcaster or they may be left in the previous world or trapped in the doorway between them. If you are certain that you know a location in this other world you are travelling to, you must think of the location you are travelling to.

Similarly like its sister spell Plane Shift, World Shift can have use of an object like a metal rod attune to that world's Mortal Plane or sister planes and use it to help cast the spell. Unlike Plane Shift however, this object can be anything that is attuned to the world but is optional when casting the spell. If you have a object that is attuned to that world, your chances of going to that certain world are always successful. If you don't have an object attuned to that world, you must roll a D20 plus your whatever ability score you mainly cast your spells through (Intelligence for Wizards, Wisdom for Clerics, etc) to make sure you and whoever you are travelling with arrive in a random world successfully and safely. The Spell DC for this roll is set by your Dungeon Master at their own discretion. 

Also like Plane Shift, if you know the sigil sequence of a teleportation circle on another world, this spell can take you to that circle. However unlike Plane Shift, you may take a gamble for the same roll as above to traverse worlds in hopes that they have the same sigil sequence or similar. If the teleportation circle is too small to hold all the creatures you transported, they appear in the closest unoccupied spaces next to the circle.

You may use this spell to banish an unwilling creature to another world if you so choose. Choose a creature within your reach and make a melee spell attack against it. On a hit, the creature must make a Charisma saving throw. If the creature fails this save, it is transported to a random location in the world if you used the spell in tandem with a object attuned to that world or a random world if you don't have such an object. A creature who is transported to another world must find its own way back to your current plane of existence. However, you must also consider the fact that there may be people of this other world you may putting in danger if you use the spell in this way, your choice may ruin the lives of those who have no part in this battle so think carefully before you use World Shift in this way.