During the battle, Frankensteinway has four phases, each with 10 health. The boss room has four electricity generators with buttons next to them that will deactivate them. Unlike most enemies, Frankensteinway is 2x2 tiles large, and any of the tiles he occupies can be attacked accordingly; be wary of this when the floor begins to pulse electricity.
In the first phase, Frankensteinway will stay idle for several beats, then move 3 tiles in a random direction, which will be telegraphed by yellow squares that show which tiles he will hit. When he begins to move, random patterns of tiles will flash with electricity, which will damage the player if they step on those tiles. During this phase, two white sarcophagi spawn at the top corners of the room.
In the second phase, Frankensteinway lost his left arm, the generator farthest from the player will turn on, and Frankensteinway will become invincible until it is turned off. Note that performing a move that would attack Frankensteinway will instead damage the player. The two white sarcophagi will respawn if they were killed in the last phase. Otherwise this is the same as phase one.
In the third phase, He lost both of his arms, Frankensteinway behaves the same as the second phase, but he will no longer summon electricity in patterns when he moves. Instead, waves of damaging electricity will constantly form and move down from the top of the room, similar to the Golden Lute's fire attack. These can be hopped over if the player is right below them; essentially swapping places. Also, the two sarcophagi will respawn again and turn yellow.
In the fourth and final phase, Frankensteinway turns red and will charge across the room cardinally OR diagonally after several beats, similar to Dead Ringer, breaking anything in his path. Much like his other moves, squares will show what tiles will be attacked; however, note that Frankensteinway moves across and attacks all these tiles in a single beat. He also stops moving the beat before he charges. Meanwhile, the sarcophagi will respawn and turn black, and the waves of electricity will continue to spawn.
Once he reaches the fourth phase, it is arguably easier to focus on positioning than clearing the enemies, and simply bait Frankensteinway into charging into his own allies and destroying them, the generators, and the sarcophagi.
At the end of each phase, Frankensteinway will spawn a random miniboss.
- Nocturna's starting Cutlass can parry Frankensteinway's attacks, making it very useful for this fight. It is also possible to destroy the generators before the last phase, either by using a bomb, a Dagger of Phasing, or (situationally) by parrying one of Frankensteinway's attacks such that the knockback forces you into one of the generators (which will destroy it). The activation of Frankensteinway's shield at the beginning of each phase (after the first) depends on the generator farthest from the player when the phase starts; if it is already destroyed, then Frankensteinway's shield will not activate.
- If an unshielded Frankensteinway is hit by a Red Dragon's fireball, he will be killed instantly without going through the remaining phases.
- Frankensteinway's name is a pun on Frankenstein and the piano company Steinway & Sons.