a).

1. Sf5! c6 2. Bc2 Kb5 (2. ... Ka6? #5) 3. Kd4

3. ... Ka5 4. Sd6 Ka6 5. Bd3+ Ka5 6. Sb7#

3. ... Ka6 4. Sd6 Ka5 5. b4+ Ka6 6. Bd3# (switchback mate).

b).

1. Sc2! c6 2. Ba7 c5 3. Kd5 c4 4. Kc6

4. ... cxb 5. Bb6+ Ka4 6. Bb5# (ideal mate)

4. ... cxd3 5. Bb6+ Ka6 6. Sb4# (model mate)

 (4. ... c3? 5. Bb6#)

Including short mates, all white pieces mate and all are used in both solutions. Passive bishop sacrifice in b.[A]