Introducing a new variant: sacrificial promotion chess

For example, if a pawn reaches the 6th or 7th line, it can be promoted, but you must sacrifice a few materials for the promotion. Such as, if you want the pawn to be promoted to a knight or bishop at 7th line, you need to sacrifice at least 4 pawns, or 1pawn plus a knight or bishop,or other equal material. If you want the pawn to be promoted to a knight or bishop at 6th line, you need to sacrifice at least 6 pawns, or 3pawn plus a knight or bishop,or other equal material. That is to say, there must be a minimum request of sacrifice for the promotion. Of course, it is ok if you are willing to sacrifice more material for a promotion,such as sacrificing a rook or queen to promote a pawn to knight or bishop. Also you can choose to sacrifice your queen to promote the pawn into a rook and so on. This rule can increase complexity for AI calculation.

The promotion is non -compulsory.If you pawn is on the 6th or 7th line, you can choose to promote it or not in this round。 This is very different from the compulsory promotion rule on the 8th line. You may not promote it within ten moves, and the engines must consider the possibility of your promotion within ten moves. The pieces are changing position every move, so the sacrifice material vary evry turn, and the engine calculation capability requirements are much higher. Of course, it is impossible to rely on this to defeat the engine calculation. The purpose here is to increase randomness in order to give human players more room and reduce draw at the same time.