Enemy: Group Boss Hybrid (Blaster)
Story: During Spec Ops 18, Princess Celestia received multiple letters about Group Boss Hybrid being overpowered and indestructible. The OP part she could understand, but indestructible? Reading that he's weak to fire and sonic attacks, Celly brings Octavia Melody and Vinyl Scratch to finish off the boss.
Special Conditions: Vinyl's radio is set to max volume, inflicting Pain Train on Hybrid every round. Also, Guitar Hero CAN crit Hybrid and exploits migraines.
Octavia has the "Come at me Ock" passive, which lets her occasionally protect allies from single-target and area attacks. While she protects allies, she blocks the attacks with her cello, taking decreased damage.
And Hybrid won't take more damage than all seven of Fullmetal Alchemist's Homunculi combined.
Battle strategy: The first action Vinyl should use is Bass Cannon, then on the extra turn, any of the weapon-grade music actions. You don't want Hybrid to crit Tavi, so have her start with Bow-merang, impairing him. Then have Celly start with Solar Beam to blind him. Though she cannot critically hit Hybrid, all her attacks will still do extra damage to him. If Hybrid gets Refocused, use Sunburn if possible. Use Guitar Hero if Hybrid hasn't removed his DoTs. Get rid of debuffs using Encore and Friendship Letters.
Empowered Iso-8: Defensive Cello Iso-8 (Octavia only) - Gives her the "Come at me Ock" passive outside of the Heroic Battle.