1 is actually already possible! By utilizing promotedFrom and restricted crazyhouse, you can have a brick royal that is unreachable from the main board, and the two pieces that you want royal are promotedFrom 'F' (ferz), while every other piece is promotedFrom 'x' (invisible brick -- can't be placed). Then, around the brick royal (with 2 lives), have two squares where players can drop the ferz w/ check, but can't move the ferz. Don't forget to turn on regicide.
There's a guide in the Club Directory detailing how promotedFrom and Restricted Crazyhouse works.
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Edit: I just reread the comment. Here's how to do it if ANY 'royal' is captured:
1. Have all the 'royals' be promotedFrom 'K', and every other piece be promotedFrom 'x'
2. Make the entire board a hill. This way, once a 'royal' is captured, the player can drop it on the board and win.
The only downside here is that you can't have a king be a normal piece.
1. multiple royal: players may have multiple royal pieces, and get mated if any of the royal piece get mated or captured.
2. weak pieces: some of the pieces can be set to have a certain number of lives (not necessarily the same number), and a piece will lose one live if it is attacked by an opponent's piece after the opponent's move. For example, two rooks staring at each other will keep losing lives. Pieces run out of lives will turn into dead pieces or empty squares. (remark: this is similar to apply the N-check rule to non-royal pieces, but with a slight difference)
3. medium squares: some of the squares can be set to be a medium square. A medium square works as if there is a dead piece on it when it is empty, and works as a normal square otherwise.
4. sculptor: some of the pieces can be set to be sculptors. In each move, a sculptor will leave a dead piece on the square it moves away from.
I may add other new custom rule ideas here later.