Oneliner, symmetrical position, asymmetrical solution, symmetrical constellation (totally: horizontally & vertically), two exchanges of roles (Nb2<>Nb4: try 1 (Nb4>>Nc3, Nb2>>Nc2#) / try 2 (Nb4>>Nc2#, Nb2>>Nc3) & try 2 (Nb4>>Nc2#, Nb2>>Nc3) / solution (Nb4>>Na3, Nb2>>Nc2#)), option key, flight taking key, minimal, model mate, symbol problem (candle), corner mate

Animation mode on PDB: https://pdb.dieschwalbe.de/P1419199