Both sides can have any number of holes on the board. The hole cannot be taken by normal move of any piece. It moves as a king and normally doesn't capture. It means normal move of hole is 1 square ortogonally or diagonally to vacant square and normally it doesn't give check. Pawn can promote to hole on last rank.
Anytime pawn is on second rank it can make double step.
All pieces including holes, but except king, can play move entering hole of own side and leaving hole of own side too, piece leaves latter with added energy, it means it can make longer move and capture any piece including opposite holes and all own pieces. Piece X is moved to square occupied by 'white hole'. Then the piece X must make move in the same direction in which it entered 'black hole', this time the move leaving 'white hole'. It is possible for this second part to be e.p. Also pawn ending its relativistic move on last rank promotes immediately.