I suspect 'cannot be placed in check' was intended to mean 'is not subject to any checking rule'. Why else call it a Commoner?
I would avoid calling the Nightrider a major pieces, as this term usually indicates pieces with mating potential. I suggest to use the term 'heavy piece' instead.
The full-file rule strikes me as odd: it tries to 'solve' the problem that on a full file there would be no room for a new Pawn, so that you could not capture a heavy piece in it, by merely making that same problem occurring earlier, when the file still has one empty square. It still seems to be a never-happens situation, but if this rule is just added for completeness, it would seem best to make it such that it only has to be invoked at the latest possible stage, i.e. that you cannot capture a heavy piece on a completely filled file. If the idea is that this gives the game an interesting twist, and should actually occur in games, it should already kick in on more sparsely filled files. E.g. half full, or when there is no empty square on your own half of the board.
I suspect 'cannot be placed in check' was intended to mean 'is not subject to any checking rule'. Why else call it a Commoner?
I would avoid calling the Nightrider a major pieces, as this term usually indicates pieces with mating potential. I suggest to use the term 'heavy piece' instead.
The full-file rule strikes me as odd: it tries to 'solve' the problem that on a full file there would be no room for a new Pawn, so that you could not capture a heavy piece in it, by merely making that same problem occurring earlier, when the file still has one empty square. It still seems to be a never-happens situation, but if this rule is just added for completeness, it would seem best to make it such that it only has to be invoked at the latest possible stage, i.e. that you cannot capture a heavy piece on a completely filled file. If the idea is that this gives the game an interesting twist, and should actually occur in games, it should already kick in on more sparsely filled files. E.g. half full, or when there is no empty square on your own half of the board.