you will explode.
Nah, Shattered and Random world are different. Shattered is still all the same historical characters, religions, cultures, etc as before, except no one can have a higher title than Duke or Count (whatever you set it for). And there is a special CB that everyone gets access to at the start of the game to let them conquer a de jure realm more quickly.I'm pretty sure Shattered start is automatically a random start. There's a bunch of settings you can play with. I should experiment with the random start settings as well, but if you go all in on the random settings in the Shattered Start menu, it'll randomize culture names, randomize religion names and traits, randomize where on the map different cultures and religions spawn, randomize the locations and names of du jure kingdoms and empires...
Random has a few different settings so you can keep historical religions or cultures but otherwise mix up characters, realms, etc. Or you can start going really, really random like new religions, new cultures, new realms, etc. There's a setting to make an Byzantine equivalent and a HRE equivalent, and other settings to make a max realm size at the start of the game. Or even a max age. There's an achievement called Lord of the Flies that involves starting in a Random world where the max age is set to zero so all the rulers around the world are babies.