I just mean having a clear place for used cards is needed. Also, when each player is eliminated, making sure they return any unused cards. I just think the odds of someone forgetting a card in their pocket and taking it home goes up as number of players go up. Counting the discards to make sure their is the correct number was easy with 1 deck, more work with 4 decks.
The ones I remember that could use examples.
Foresight: I don't even know if this is what you intended, but it was generally used to place yourself into the group of 3 (which was always group 3). That was not obvious to everyone at first.
Possess Object: There was a question about this. I think having 2 examples written would be good.
e.g. 1) Alice casts Possess Object on Bob before the round begins. Gift from the gods is randomly selected, and Alice forces Bob to make Alice invincible.
2) Alice casts Possess Object on Bob before the round begins. Heal, Self is randomly chosen. Since the they are in the before round begins phase, the spell fizzles and is discarded.
I think Shatter, Global has issue, because many spells are cast that the player holding the card is not aware of. They might potentially want to counter a bootstrap paradox in another group, but not even know it was cast, or they might be playing at the time.
Couple other thoughts I am remembering now.
What is the rule if 2 people roll a critical hit (or any tie a guess)? It should be written down that the original order stands and they reroll to break the tie (of course maybe it was and I missed it).
How strict do you want to be about spell fizzling (sorry, I grew up playing magic in highschool). We were very lenient, basically, people could not cast at the wrong time outside of Possess Object.
I will draft what I think a TD guide should be in a doc and share it send it to you. If you think it is reasonable and matches your vision, it can be either turned into a Wiki or published as a link here.