Hint 1
Black must avoid checkmate.
Hint 2 (a very big hint)
Black's e pawn.
Spoiler
https://www.chess.com/analysis/game/live/122884427351?tab=analysis&move=72
e1=N+ - underpromotion!
Underpromotion is very rare. The key thing is it's a check and a check is a tempo which is a very important concept in chess. Why not a queen? No tempo :( so white has checkmate in 3 starting with Rc8+.
I watched this speed chess game live and the move happened even before I thought about underpromotion. I wonder how long it would have taken me to see it in a slow game.
"Vimes had never got on with any game much more complex than darts. Chess in particular had always annoyed him. It was the dumb way the pawns went off and slaughtered their fellow pawns while the kings lounged about doing nothing that always got to him; if only the pawns united, maybe talked the rooks round, the whole board could've been a republic in a dozen moves." (Terry Pratchett, Thud!)
- Play a Swamp
- Pass the turn
- In white's end step, tap the Swamp and cast Fatal Push, targeting the opponent's king
- Chess pieces have no mana cost, so black wins
I had that move in mind, but I didn't see the underpromotion. Brilliant.
