We recommend using the Thunderstore Mod Manager or an alternative for installing mods
Allows you to enter a custom run seed in lobbies. In multiplayer, only the host can set the seed.
If the custom seed field is left empty, the game will generate random a seed like normal.
Thanks to KingEnderBrine for his Random character selection mod which helped me figure out how to add UI to the lobby correctly.
Thanks to Ulivax for help testing this mod!