I have this problem with all my design. The design process goes at follow (of course, the process is iterative):
Step 1: You have an idea, you take down notes. It's basically an exploration step, you might not get playable game idea.
Step 2: You put those notes into rules. They could be incomplete rules, but you have an idea how the game could be played at this step.
Step 3: You create content to be able to play test the game. This is where I am blocking.
Step 4: Create a prototype
Step 5: Refine the game until completed.
At step 3, this is the step where I should do what I call protorushing and start creating some content to be able to play the game.
For example, for my investigation game, I would need to design a few characters, many encounters, a demon, and a few other components to start playing the game. I don't have to do everything, but enough to be able to play.
But I have some kind of designer's block and cannot proceed further. From what I know, methods I know so far:
Use another game as a source of content: I Did this for eldritch express, by using arkham horror database. It's the easiest method, but not always possible.
Improvise: Good for limited content, but imagination can run out rapidly, and you might not explore the entire possibility space.
Chat GPT: This is a technique I am curious to try. I intend to use it only for brainstorming. Putting mechanics or stats on a thematic idea seems easier than doing the opposite (theme on mechanics). It could avoid trying to generate all stats permutation and slapping a theme to each combination. Making it less bland, and more fun to design.
Toy play + generator: Generate content as you play, this is another possible technique that use improvisation, but while playing instead of improvising in advance. Solo RPG generator tools could also be used to help.
Do you have other ideas on how to generate game content?
I am already taking notes, reading everything, and putting it in a rule book draft. When I have those rules I want to test, I need content, not rules.
For example, I have a Vampire Survivor concept to implement as a deck building game. I made some card cycling tests with regular cards. But if I really need to test the game, I need cards, therefore monsters, equipment, spells, etc. That is the stuff that is hard to design.
Even abstract games have content. Take for example dominoes, there is a choice on how they distribute the numbers on the tiles.
Prototypes can be ugly, especially at early phases, I don't care. This is why it`s called a prototype. Scavenging components is a classic method in prototype design.
My hypothesis, is that if I have thematic background, it could make it easier to design the content. If for example, you give me a list of monsters to put on cards, It might be easier to put stats on those monsters. On the other hand, if I just want to put stats on blank cards, it could be more complicated.