White captures: axb, bxa, cxbxa, xBc8, gxf/hxg, Rxc2+ = 8. Black captures c/e7xd6. So balance made, and no spare captures possible. If c7xd6 then e-pawns collide, so e7xd6 & wPe>e8=. So bPc either promoted on c1 or was captured on c2.
R: 1.Rd/e2xZc2+ If Z just moved, then it must have been responding to c2xb3+. But this would block bPc>c2>c1, so Z did not just move. Also bK did not just move; so by elimination R: 1... g2-g1=B. Now R: 2. Sd1-b2+? because of wBa3 illegal check. So the only possibility is Staugaard castling. Thus R: 1.Re2xZc2+ g2-g1=B 2. 0^6+! g3-g2.
Z=Q,R,S would render Staugaard illegal. Z=B requires too many Black pawn captures. Therefore Z=P, which must be original bPc.
Note the black bishop on g1 is a bonus phoenix! See https://en.wikipedia.org/wiki/Black_bishop.
White captures: axb, bxa, cxbxa, xBc8, gxf/hxg, Rxc2+ = 8. Black captures c/e7xd6. So balance made, and no spare captures possible. If c7xd6 then e-pawns collide, so e7xd6 & wPe>e8=. So bPc either promoted on c1 or was captured on c2.
R: 1.Rd/e2xZc2+ If Z just moved, then it must have been responding to c2xb3+. But this would block bPc>c2>c1, so Z did not just move. Also bK did not just move; so by elimination R: 1... g2-g1=B. Now R: 2. Sd1-b2+? because of wBa3 illegal check. So the only possibility is Staugaard castling. Thus R: 1.Re2xZc2+ g2-g1=B 2. 0^6+! g3-g2.
Z=Q,R,S would render Staugaard illegal. Z=B requires too many Black pawn captures. Therefore Z=P, which must be original bPc.
Note the black bishop on g1 is a bonus phoenix! See https://en.wikipedia.org/wiki/Black_bishop.
