There is no ceiling collision above a certain level in the starting tunnel. If you look straight, you'll see a clearly defined triangle which you can just phase through. Then navigate out of bounds to the last boss!

Items used:

• Wearing: Onyx Amulet with Wind Sculpting Stone & Harmonic Music Stone, 3x Azerite Armor with the Longstrider trait, Scroll of Momentum, speed enchants
• Before entering: Fried Bonefish, Charged Phial of Alacrity
• During run: Nitro Boosts, Quickwick Candlestick