Elk changes to knight or rook, Elkrider to rook or nightrider, depending on the color of its square. Gary Gifford's remote sensing mimic pieces used in Remote Sensing and Remote Sensing with On and Off Board Detection, also have their movements contingent upon the color of the squares upon which they are situated.
The Spearmen, also used in Mark Hedden's Ganymede Chess, can change from one type of bidirectional line piece to another at the end of their move. Or they can rotate / switch without moving. The strength of optional mutability in spearmen is weakened by the fact they can only capture when moving forward.
If I understand correctly, changes in polymorphic pieces in Polymorph Chess always count as moves in themselves (apart from Black's option to make one of four sets of switches in the beginning).
These polymorphic pieces remind me a little of the Spearman from John William Brown's Centennial Chess and of Mats Winther's Elk in Elk Chess (with Scorpions) and Elkrider in Elkrider Chess.
Elk changes to knight or rook, Elkrider to rook or nightrider, depending on the color of its square. Gary Gifford's remote sensing mimic pieces used in Remote Sensing and Remote Sensing with On and Off Board Detection, also have their movements contingent upon the color of the squares upon which they are situated.
The Spearmen, also used in Mark Hedden's Ganymede Chess, can change from one type of bidirectional line piece to another at the end of their move. Or they can rotate / switch without moving. The strength of optional mutability in spearmen is weakened by the fact they can only capture when moving forward.
If I understand correctly, changes in polymorphic pieces in Polymorph Chess always count as moves in themselves (apart from Black's option to make one of four sets of switches in the beginning).