Let's look at this position white to move. Assume that it continues:
1. Ng4 b1J (chooses to promote to Joker)
At this moment the black Joker imitates the last piece that white had played and that's a Knight.
So the white Joker now imitates whatever piece the black Joker is imitating, again a Knight.
If the opponent has promoted a pawn, the Joker inherits movement and normal capture abilities from the piece it promoted to.
I found another inventor of the Joker who implemented this point in the same way here:
http://www.talkchess.com/forum3/viewtopic.php?f=7&t=51616
I came up with a new scenario that still must be clarified:
White moves a pawn to the last rank and promotes the pawn to a Joker. Now it's Black's move and Black has a Joker. What is Black's Joker now imitating?
I'll give this a thought.
Maybe it could pretend to be a pawn...
I agree