It is the creator of the game that determines what assets are available in it, not the GM. That being said, this refers to the assets that can be shared, not the assets that the player has access to. I have a game created by my dummy account, which is a free account. I can access all of my paid content while logged into the game. If I were promoted to GM, I can even drag in MM monsters instead of the SRD versions. None of the other players would be able to look that info up in the Compendium tab, though, and the original creator would not be able to drag in Compendium monsters, though they would be able to use ones that I had dragged in. I would not be able to run say, Rime of the Frostmaiden however unless A) I owned it and created the game, or B) the other player owned it and created the game then promoted me to GM. If you want to do any testing, create a Dummy Account , and have it create a game and invite you to it. You should be able to figure out what you can and cannot do. In the specific instance you note above: Account #1 = Adam Account #2 = Betty Adam has purchased only the core rulebooks, created a game and invited Betty to be GM. Betty has no core rulebooks, but has purchased Xanathar's Guide to Everything , which has rules for Goliath characters. Other players would be able to create characters using all of the assets from the Core books, assuming sharing was turned on, but would not be able to access the Goliath Compendium info in Charactermancer. Betty could create a Goliath character but not the players or even the creator of the game could do so. Adam and players can use (game creator) Adam's stuff, but not Betty's Betty would have access to everything from Adam and Betty in that game.
