Mike Nelson's criteria look right on track. One could add that Chess on a
Longer Board is not an Ultima Variant simply because the Withdrawer isn't
too weak in CLB, although I guess a King, a Withdrawer, an orthogonal
Coordinator, an orthogonal Immobilizer, diagonal Chameleons, Jumping Chess
Knights and Pawns stepping one or two squares vertically forward but
capturing custodially diagonally would still add up to an Ultima variant.