The terms of service make no difference between public and private games.
You probably shouldn’t make these dark themes on Roblox until there are proper age-gating features. It’s not the right platform for this at the moment and you will be shut down if moderation finds the game. Moderators can inspect private games.
I use this one line in any rules I usually make,
“If you have to ask, it’s probably not ok” 
Building a Hanging Man for the game Hang Man is probably acceptable.
Building a Hanging Man as a threat to a Roblox Player, Group, or Community is absolutely going to be moderated.
As you came here and asked, I think you will need to read through the Roblox Term’s of Service more often to be more aware of moderation.
I hope this finds you well.
I don’t think it is a threat, just something that ‘enriches’ the story and the narrative. You are right though, there is a line and this I think will cross it.
Happy birthday!
Cheers for the support!
I will take action.
Is this actually something bad for the environment?
Because i find these kind of things some times when i visit games everywhere, they are actually fun to watch.
From previous emails with Roblox support, it seems that trying to convert someone to another religion or other belief or group is against the ToS, no matter if it’s a joke, role-playing, or serious.
This is useful to know!
I’m not so sure that this will be acceptable.
There’s a rule I follow when doing something and it’s quite helpful:
DON’T BUILD ANYTHING THAT’S QUESTIONABLE
It’s the easiest way of not getting in real trouble with your builds.
If you have to ask then you probably already know the answer. If anything, having that in a game on Roblox seems pretty edgy to me and I have to question how you even remotely got the impression that this would be a good idea.
