SPARTAN CHESS

Rules of FIDE chess, except:
Start with 30 pawns and 2 kings each (at d1e1/d8e8)
Goal: capture both opponent kings.

1222... progressive mutator. The two moves in a turn must be made with different pieces.
If one king is captured, the victim goes down to 1 move per turn.
Pawns may move 2 steps off 1st or 2nd row at any time, e.p. applies.
Whenever a piece makes a capture, it goes UP a step in power,
using the sequence P>N>B>R>Q>A(=QN). 8th-rank pawns promote to A.

Game sample:
                       White        Black
p . p k k p . p  1.  ---  d:e5   d:e5  g:f4
. p p p p p . .  2.  e:f4 e:d5   e:d5  N:d3
. . . . . p . b  3.  g:h5 a:b5   a:b5  g:h5
. . N . . p p .  4.  b:c5 c:d3   b:c5  n:f4
. n n . . O . .  5.  N:f4 c:d5   c:d4  h5  
. O K O O O O O  6.  a4   c4     N:f4  Nd4
. . . . . . . O  7.  g:f4 e3     N:a4  N:b3  
. . O . K O O O  8.  a:b3 N:h5   B:b3  g6
---------------- 9.  B:g6 a2     h:g6  Rb6
                10.  c3   f4     N:h4  a4
                11.  b:a4 Kc2    Rb4  Bg5
                12.  b3   g3     Bh6  b5
                13.  Nc5  d3     b7   g6  
                14.  a3   f3     a5   g5
                15.  a:b4 Kc3    a:b4 b:c4
This is a very enjoyable game, with lots of capturing action starting at turn 1, and then shifting to subtle positional battles in order to promote to Amazons (Queen + Knight power). The fact that each player has two Kings also add an extra complexity of trying to protect both for as long as possible.