The Elf explained

The Elf moves and captures like an Amazon (Queen - Knight component) however:
When the last move by the opponent was a capture, the Elf can only capture.
When the last move by the opponent was a move without capture, the Elf can only move without capture.

Examples

Black to move. If Black plays Rf1 then the white Elf is trapped, as Exf1 is not allowed.

White to move, White is in check. Kxf2 is not allowed, because that would put the white King in check from the Elf.

Black to move. Black is in check. It's true that White is not allowed to make a capture, as the black Elf would then immediately be giving check to the white King.
Nonetheless also Black is in check in this position.

White to move. If White plays Nb6, the Black Elf is lost. Nb6 is a non-capture, so the black Elf cannot escape the threat of the Rook. ExR is not allowed, and neither is ExN.

Black to move. Here, cxb4 or axb4 wins the Elf and the game. Because the Elf cannot do a non-capture move to avoid being captured.

Elf and other advanced pieces

If the last move done by the opponent is a special move, and it is neither a normal capture, neither a normal move, then the Elf can neither capture nor move. You must play another piece. Time thief-like capture is an example of such a move. Another example is the Metamorf going to another form.

Interesting piece. What do you estimate its value is? I doubt it would be useful in the endgame.

Hi, this piece is very interesting in deed. I assume that it's value devaluate the more pieces are traded. It's very difficult to give a value for it. All depends on the position and the last move played. It's a piee that brings for sure many surprises to the game. I will try to add it to my Musketeer Chess version 1.5. Probably average value will be the value of a King which means 4 points but it can be a useless piece in some positions and a very very strong piece especially in open positions were it can capture other valuable pieces such as the Queen or Rook and can also restrict opponents choice !

Really excellent imagination !

There have already been played several rated Bulldog games with this piece. All ended with Elf-related tactics.

In deed, i see enormous possibilities with the Elf !!

It's probably even more stimulating than the Witch or Angel !!

Are you the inventor of this piece?

I invented it here. Games here, here and here.

I've added one more example in the OP.

So it can protect any piece of your on the board easily

Correct

Oh, shoot!! I have to create a 3D model for him...

Wait wait wait if you expose your opponents king you can protect anything with it

What the hail

İts op

İts around the power of amazon

The Elf is not very strong. You neutralize him by just not capturing anything so he can't capture on the next move. It adds little to mating power in the endgame.

As long as your King is in the line of sight of an enemy Elf, you cannot ever perform a capture, no matter how gainful that capture could have been. This is because, if you capture, your King will be captured by the enemy Elf, thereby ending in checkmate.

The two exceptions to this are

1 - that the capture somehow results in blocking the enemy Elf from seeing your King within his line of sight

2 - that the capture was on the enemy Elf himself.

I suppose we both have a slightly different idea as to what makes a piece strong. For me, if your Elf is causing your opponent to be wary about performing capture on you, so much so that he/she is avoiding it in certain situations, that's some pretty powerful maneuver right there.

You Just need to expose the opponents king to make all your pieces invulnerable