For my vote, I would be more than curious (now that the idea of Immobilizers has come up) to see Demigorgon Chess,
or Medusa Chess. It was invented by Vernon Rylands Parton in the 1960s, and it is a great variant. The text on the games, including Alice Chess and several others, are located in a Text File at ChessVariants.org, in reference to several pamplets on chess variants, both 2d and 3D, and some draught-based variants as well. Look under the section on "Demigorgons" on pages 4-6.