The big omission I see: can an Immortal capture on the move it's brought in with?
While bringing them into the game players have to make sure that they are moved at a safe distance from both Kings, so that no King will be in check
Is this an extra rule? Ensuring your own king won't be in check makes sense, but you've nowhere else suggested that it would be a bad idea to potentially check the opposing king, unless this is supposed to tacitly forbid that
I am not sure if anybody has ever tried before to use chess pieces with hidden identities
The Disguised Pieces tag has a couple games that might be similar; Thesetwo probably come closest, though neither goes quite as far as your Immortals
The big omission I see: can an Immortal capture on the move it's brought in with?
Is this an extra rule? Ensuring your own king won't be in check makes sense, but you've nowhere else suggested that it would be a bad idea to potentially check the opposing king, unless this is supposed to tacitly forbid that
The Disguised Pieces tag has a couple games that might be similar; These two probably come closest, though neither goes quite as far as your Immortals