The Werewolf explained

Inventor: @HGMuller

https://www.chess.com/forum/view/chess960-chess-variants/werewolf-chess

The Werewolf can slide like a Queen but over a maximum distance of 3 squares.

If the first square is occupied, then the Werewolf can leap to the second square, but not to the third square.
If the first square is occupied by an enemy piece, then the Werewolf can optionally capture that enemy piece while leaping to the second square. This makes the Werewolf capable of double capture.

Example

The white Werewolf is attacking squares e5, e6 and e7, but not giving check on e8.
The white Werewolf could leap to g4, but not to h4.
The white Werewolf could leap over d5 take the pawn on c6. It could optionally take on d5 and then on c6. It could not leap to b7.
The white Werewolf could leap to c2.
It would be capable of taking on d3 and then moving on to c2, but then again this is not possible, because this would put the white King in check.

The Werewolf is contagious to all pieces but the King. This means that any piece becomes a Werewolf when it takes a Werewolf (but a King taking a Werewolf remains a King):

In this position, White to move, White could safely play 1. WWg4.
In a continuation 1. ... hxg4 2. fxg4 Nxg4 3. Nxg4 white would still end up with a Werewolf on g4.

This rule for contagion comes from Maka dai dai shogi. Any piece that takes a Teaching King or a Buddhist spirit, promotes to a Teaching King or Buddhist spirit respectively.
In the Halloween Challenge Tournament, @Marks1420 introduced a version of the Werewolf without contagion rule.

Suggestion for notation:

WWf3 does not capture any pawn.

WWxe3 - f3 captures the pawn on e3. 

WWxf6 captures the pawn on f6, but not the pawn on e6

WWxe6xf6 captures both the pawn on f6 and the pawn on e6.

Interactions between Werewolf and other special pieces

In general, all pieces, also magical pieces, are subject to Werewolf contageon. At least definitely this is the case for Metamorf, Time Thief, Joker and Dwarf.

However, the Angel grants immunity to Werewolf contageon. That means: When a piece takes a foe Werewolf on a square where a friendly Angel grants immunity, the piece won't turn into a Werewolf.

A Spirit never turns into a Werewolf but remains intact.
- A Spirit possessing an allied Werewolf results into a possessed Werewolf
- A possessed piece taking a Werewolf, if the underlying piece is subject to contageon, results into a possessed Werewolf

very nice explanation 

Nice explanation.

I have a suggestion regarding notation. How about using "x" when the werewolf captures one piece and "xx" when the werewolf captures two pieces.

Example:

WWf3 does not capture any pawn.

WWxf3 captures the pawn on e3. 

WWxf6 captures the pawn on f6, but not the pawn on e6

WWxxf6 captures both the pawn on f6 and the pawn on e6.

Of course if someone writes something like "WWxf6 and capture the pawn e6" that would be accepted as a double capture too.

That seems really very counterintuitive. Intuitively, I interpret "WWxf3" as "a piece abbrieviated as WW captures something on f3 and ends there".

Rather, I can investigate if some convention exists in large shogi variants for notation of double capture. After all, that's where this is coming from.

I have this suggestion and it is supported by the Middle Shogi Manual where it describes complex Lion moves:

Example:

WWf3 does not capture any pawn.

WWxe3 - f3 captures the pawn on e3. 

WWxf6 captures the pawn on f6, but not the pawn on e6

WWxe6xf6 captures both the pawn on f6 and the pawn on e6.

so this is the new notation rule?

If yes, it doesn't affect ongoing tournaments with Werewolf, right?

In ongoing games you would just describe in plain words what move you intended to play. My opponent posted "WWxi7" with a Werewolf on g7, and in a later post claimed that he had also taken on i7. I had rejected that.

Oh ok.

This notation looks good to me

which game is that btw?

I've added this notation suggestion to the OP

https://www.chess.com/clubs/forum/view/bulldog-chess-witch-and-werewolf-deeper-thinking-evert823

ok

I want to add this to the descriptions. Looking forward to comments if any. Without objection from anyone in coming 3 days I will add it .

Interactions between Werewolf and other special pieces

In general, all pieces, also magical pieces, are subject to Werewolf contageon. At least definitely this is the case for Metamorf, Time Thief, Joker and Dwarf.

However, the Angel grants immunity to Werewolf contageon. That means: When a piece takes a foe Werewolf on a square where a friendly Angel grants immunity, the piece won't turn into a Werewolf.

A Spirit never turns into a Werewolf but remains intact.
- A Spirit possessing an allied Werewolf results into a possessed Werewolf
- A possessed piece taking a Werewolf, if the underlying piece is subject to contageon, results into a possessed Werewolf

what if the second square is occupied?

Can the werewolf capture the pawn?
(the pawn that has a knight between it and the black werewofl)

No, the WW can't jump to the 3rd square.

ok.

Hi HG

In the first diagram, the warewolf can capture on d3 but cannot move to c2 because it is pinned. If there is no black bishop on the a6-f1 diagonal your double move capturing d3 and then moving to c2 will become possible.

The warewolf is really a fun piece to play with, like the Witch. The main interest of these pieces is that they are tricky and need some time to understand their inner tactics. This makes the games very entertaining and surprising. One can also learn a lot.

For the Board Painter users, here is the icon i recommand for the Warewolf

I think that if a possessed Werewolf is captured, the Spirit that was possessing the Werewolf will be taken from the board. And then still the piece that did the capturing will become a Werewolf if contagiousness was applicable.