After move 87. Rc2 Ba4+; unprotected bishop skewers the king and rook. Not taking the bishop loses the rook and possibly the knight next. Taking the bishop leads to mate in 1.
I unfortunately came second in my pool so this was the final move of my final game due to resignation. Not a bad way to finish.
Full Game from Round 2: https://www.chess.com/analysis/game/daily/490158251?tab=analysis