Magnus Carlsen new chess variation: he trolled his team in this video

Wait - it says check so it's a knight. So how is it controlling d8 and being "still" a bishop at the same time? There's a hole in this logic.
Besides, after B/N (whatever) takes b7, couldn't the Bc8 just grab it?
Wait - it says check so it's a knight. So how is it controlling d8 and being "still" a bishop at the same time? There's a hole in this logic.
Besides, after B/N (whatever) takes b7, couldn't the Bc8 just grab it?
He didn't explain it well at all.
I think he means after your move it changes. So after 1...Nf6 all black's minor pieces have changed. So after 2.Bxb7 black's c8 piece is still a knight until after black's 2nd move so b7 was undefended.
But if this is true, then in the final position when Carlsen claims mate, black should be able to play Bxc7 (because black's b8 piece is a bishop).

The Bc8 would be a knight, so it wouldn't be able to take.
In the end the point is that if he moves his king to d8, then the knight on c7 will become a bishop on Magnus's turn, when black would be in check.
The Bc8 would be a knight, so it wouldn't be able to take.
In the end the point is that if he moves his king to d8, then the knight on c7 will become a bishop on Magnus's turn, when black would be in check.
If all the minor pieces change on every half move, then white's 2nd move is not possible.

<001101001> Now this is clearer, I think - but now - <Elubas> - wait: if the knight on c7 will be a bishop next move, then the king on e8 is not in check... is it?
So - There are eight knights on the board in the beginning, and every time a player moves one of the them (or maybe every time a player moves at all?) all eight minors become bishops?
Too confusing for words - and you see why GM Agdestein is laughing at that point in the video...

More than Magnus trolling some hapless GM - this is more about MARCO trolling all three of us, I get a feeling...
<001101001> Now this is clearer, I think - but now - <Elubas> - wait: if the knight on c7 will be a bishop next move, then the king on e8 is not in check... is it?
So - There are eight knights on the board in the beginning, and every time a player moves one of the them (or maybe every time a player moves at all?) all eight minors become bishops?
Too confusing for words - and you see why GM Agdestein is laughing at that point in the video...
If it alternates 8 knights and 8 bishops then b7 was defended on move 2, so this seems incorrect.

"But if this is true, then in the final position when Carlsen claims mate, black should be able to play Bxc7 (because black's b8 piece is a bishop)"
I think you're right, actually! Unless I'm counting it wrong. But it seems like every time white moves, the b8 piece becomes a bishop when it's black's turn. That pattern shouldn't change I don't think.

"wait: if the knight on c7 will be a bishop next move, then the king on e8 is not in check... is it?"
On black's move, the piece is a knight, so he's in check. But moving out of check won't do, because he'll then be in check on Magnus's turn, which is never allowed in chess. So I would say ...Kd8 should be illegal for that reason. So the idea was that black had no legal way to get out of check.
But as binary pointed out, it looks like ...Bxc7 is perfectly legal there.

The Bc8 would be a knight, so it wouldn't be able to take.
In the end the point is that if he moves his king to d8, then the knight on c7 will become a bishop on Magnus's turn, when black would be in check.
If all the minor pieces change on every half move, then white's 2nd move is not possible.
White's piece is a bishop on his turn. That gives him enough time to take on b7 before it becomes a knight.

The Bc8 would be a knight, so it wouldn't be able to take.
In the end the point is that if he moves his king to d8, then the knight on c7 will become a bishop on Magnus's turn, when black would be in check.
If all the minor pieces change on every half move, then white's 2nd move is not possible.
White's piece is a bishop on his turn. That gives him enough time to take on b7 before it becomes a knight.
Or wait. Yeah ok, I guess after black's ...Nf6 white's bishop on f3 becomes a knight :) Yeah, looks like Magnus is trolling and hoping we won't catch it :) Which I didn't :)

So what - with white to move all minors are always knights, and with black to move all minors are always bishops?
So yes, the final move WAS mate after all...
Piece to c7 CHECKS the king - which can't move to d8 because the piece is now a bishop - but next move the c7 piece could CAPTURE on e8... what a mate!
But it should mean (maybe) that white to move always wins (black could try ...c6 on move two though)

Hmm. Yeah I think you can only change your pieces with your half move. So Magnus's knight became a bishop because it was his move. Black changed his own pieces on his half move, but not Magnus's. Because otherwise, as binary pointed out, Bxb7 wouldn't be possible. Black's bishop on c8 was a knight because black changed it to a knight with his ...Nf6 move. Only after black plays ...Bxb2 does he change his knight on c8 back to a bishop, in which case it's too late obviously.

Right - something doesn't click... Magnus plays KNIGHT to f3 on move one - so he's not supposed to be able to play that piece as a BISHOP on move two.

The rules just aren't clearly defined, that's it.
I think it works under the definition I gave, and it's consistent with how Magnus was playing. You change your pieces every half move, but not your opponent's. He didn't explain it well though, that's for sure.
The cute point is that if black were to try ...Kd8, he does turn his b8 knight into a bishop, but when he's in check on Magnus's turn, black can't solve the problem by playing ...Bxc7, since it's Magnus's move... thus ...Kd8 had to be illegal previously (since it would create an impossible situation) and he was in fact mated.
I TOLD YOU!!
Chess is all about TROLLING your opponent!
I wrote about it in the following thread:
https://www.chess.com/forum/view/off-topic/chess-is-all-about-trolling-your-opponent-my-conclusion-and-i-have-proofs
Now I see Magnus Carlsen making a new kind of trolling in chess, as he teaches in this video: