Perfect Pitch

Beat the DJ Mole with a chain in which the Tuning Fork rings.
How to find it, step by step
- Play NEON ARCADE and draft TUNING FORK.
- Reach the boss and bring it to its final BONK.
- Make sure the KILLING chain (the one that lands the final BONK) features that piece.
- The defeat changes: the piece bows beside the boss, the boss says a special line and a SECRET ENDING! chip appears.
Reward
Lore: the DJ built his speakers to drown out one pure note. The Tuning Fork found it, and the whole floor sang along.
Tips
In-game hint
The DJ fears one note above all.