The Intro, Setup and most of the Pieces sections are fine. Overall, the concept looks promising. However, the Rules section still leaves out many crucial details, such as the following:
Does the Black Swan Event refer specifically to a group of pieces resulting from turning into Black Swans or Pawn promotions?
If not, you can call any group of one, two, or three non-King pieces a Black Swan Event.
Does "it cannot be placed on the board on the Black Swans' starting position, in order to avoid capturing" mean that Black Swans can only be placed on the third or fourth ranks?
This should be in the Rules section.
Can Black Swans make a double step on their first move?
If so, if a Black Swan from the first rank turns into a Black Swan after moving to the second rank, does the new Black Swan:
have the ability to make a double step?
If not, then a problem arises from having to keep track of which Black Swans started where.
have immunity from capture?
Same questions apply to Black Swans being dropped on the board due to Black Swan Events, if they can be dropped on the first or second ranks.
How am I supposed to determine the number of pieces that results from a Black Swan Event, such as:
a Black Swan turning into another Black Swan?
do the probabilities from Pawn promotions apply here as well?
promoting a Pawn?
Are pieces that are dropped on the board always Black Swans, or can the player choose which piece appears?
Does "nearby empty squares" mean anything in particular? If not, this phrase should be omitted or replaced with "square(s) on own half of board".
What happens if all pieces are on the board, or all available drop spaces for extra pieces are filled up?
The Intro, Setup and most of the Pieces sections are fine. Overall, the concept looks promising. However, the Rules section still leaves out many crucial details, such as the following: