To extend Tony's analysis somewhat: Let's limit this dicussion to
non-divergent pieces. We could, of course define a piece that makes a
non-capturing Knight move, captures as a Bishop, and observes as a Rook,
but relays are compicated enough.
Piece below means non-royal, non-Pawn piece.
There are four types of interaction:
1. Relay: the unshared move powers are added to the target piece.
2. Anti-relay: the shared move powers are taken away from the target
piece.
3. Contra-relay: the unshared move powers are taken away from the target
piece.
Relay and Anti-relay can be combined. Anti-relay and contra-relay
combined make an immobilizer. Relay and contra-relay would cancel out.
The interaction may be:
1. Direct: the observed piece is the target.
2. Indirect: the observer piece is the target.
Direct is the default.
The interactions may apply to
1. Enemy: only enemy pieces affect each other.
2. Friendly: only friendly pieces affect each other.
3. Bilateral: all pieces are affected.
Friendly is the default for relay, and enemy is the default for anti-relay
and contra-relay.
A piece might have both indirect and indirect effects, and mioght have
different effects on friends and enemies.
Effect are not recursive--in bilateral direct relay, for example, if a
Knight relays a Knight move to a Rook the Rook does not relay Knight
powers.
Only powers the piece does not have intrinsically can be added, only
intrinsic powers can be taken away. So in friendly direct relay, enemy
direct anti-relay, if a Queen is observed by both a friendly Bishop and an
enemy Bishop, the enemy Bishop takes away the Queen's Bishop move and the
friendly Bishop cannot add it back.
I have hacked together a ZRF for my first game in this genre. It is Enemy
Indirect Anti-relay Grand Chess. This is a strange but playable game. A
piece can only capture another piece if they share a move type by using a
shared move type (Queen can capture a Rook with a Rook move but not a
Bishop move). Attacking a piece with a move you can't use to capture
results in the loss of that move type. Interesting levelling effect--a
Knight can move into the path of a Queen and the Queen is immobilized.
I am considering adding friendly direct relay to the game.