Chess960 puzzles: Defensive exchange

The defensive exchange: your opponent's attack runs on one specific piece — trade it off, and the storm dies down. Find the "engine" of the attack, the piece without which the mating threats stop working: usually the queen or an invading knight. Offer the trade even at a small cost — your king breathes, and the material comes back later. The mistake is greedily dodging the exchange and getting mated a pawn up.