Constellation36: No need to message me, I still read that forum ! Questioning the promotion rule in Ambiguous Chess sounds very valid to me, since it is an important part of the game and I adopted it only after switching back and forth.

At first I didn't even think about it : I had "normal" promotions, i.e. by the piece owner. But a friend made me notice that it was not very consistent with the variant : the opponent is supposed to choose between all moves leading to the same square, the different promotions are (in my view) different moves leading to the same square, so the opponent should be able to choose the promoted piece.

That is for the logic, but then one must see how it plays in practice. That it weakens promotion combinations in the middlegame proved to be of almost no concern. Ambiguous Chess has its share of surprising combinations (especially but not only mating attacks), and frankly I don't think it needs queen promotions in order to spice the tactics.

The endgames are another story though. True enough, promotions chosen by the opponent make a material advantage a lot tougher to convert. A pawn is already more difficult than usual to lead to promotion, and then with the current rules, achieving the promotion is far from putting an end to the game.

I was afraid that it would make most endgames draws, in which case my promotion rule would be a bad one. I don't think that it is the case. Due to abandoning the stalemate rule, almost all pieces-only endgames that are wins in Standard Chess are still wins in Ambiguous. Did you know that even two same-colored bishop were enough to win against a bare king ? I think it makes the future of a material advantage look less bleak.

So unless my assessment of the endgame winnability is wrong, it comes down to a matter of taste. Should one have lengthier endgames, when the result might be the same, except a faster one, with the normal rules ? I like endgames, so I was tempted to answer yes, but I tried not to make my personal tastes account for too much in the balance. In the end, "all other things being almost equal", I just prefered to stick with the more logical and compact ruleset.

If you still can't stand the absence of queen promotions, check the two last diagrams of the following article : http://www.brainrook.com/archives/26-Just-one-more-chess-variant.html#extended