Mockery Chess

The game obeys to the same rules as orthodox chess, but the ability of pieces to “disappear” by mimicry in their close environment when they feel danger. The aim is to checkmate the enemy King with a visible piece or capture him with an invisible one (in the sense explained below).

Setup

A usual setup is needed, with possibly some markers to identify "invisible" pieces (see below). I personally used coins placed under the pieces.

Pieces

The usual pieces are used.

Rules

The additional rules are as follows:

1/ A piece under attack (King included) may “disappear” (no more subjected to attack, but still on the board) if placed adjacent to a friendly piece, already there or closing contact with it next move, in order to avoid the attack ; by corollary, a piece isolated or with only adjacent enemy pieces cannot merge with its environment and disappear. Once the attack threat vanishes (the attacking piece is removed, for instance) or the supporting friend piece is captured or moved away, the invisible forced piece recover visibility at once. 

2/ The square “previously” occupied by the disappearing piece cannot be crossed nor occupied (pieces possibly behind are not seen either and thus not attacked).

3/ A piece already invisible cannot support another piece to become itself invisible; by corollary, if more than one piece that support each other are attacked, they can’t become invisible, unless other friends support them.

4/  A piece made invisible can itself attack as a predator an enemy piece (a visible one), and possibly capture it, remaining invisible if its neighbourhood allows it. In that case, the piece attacked by the “invisible piece” can’t realise being under attack, and thus can’t disappear. The attacked King makes no exception to this rule, but as he can’t realise being “Checked” by the invisible piece, he may be captured by the invisible piece (as well as checkmated by a visible one) to end the game.

Notes

The game promises to be much more positional, and the defence much stronger, as in orthodox chess. 
The strategy seems to isolate the adverse King by destroying his close defenders, or approach him being invisible to capture him.
It has something of “Alice Chess” in it, but here shifting from one state to the other (visible-invisible) is governed by strategy, not by mandatory move (of course, “Alice Chess” is also driven by strategy !).  
Practically, one has to put some checkers (coins,…) under the “invisible” pieces.
The practical difficulty is to control every move, some pieces becoming invisible while other recover their visible state.
A last remark: "invisible" doesn't mean the piece is no more seen by the players, but that the piece is temporally no more subjected to the attack.

I wanted to changed the Game name to "Mockery Chess", following the judicious advice of L.Smith, but I realized that a "Mock Chess" already existed ! So I kept this one...