Down in the Sewer area near the train track entrance; it is sitting on your left as soon as you walk down the stairs.
It is widely considered the "UV Spectrum" bunny . The Strategy: Equip your UV Light before entering rooms. Bunny No 06
You should stack Skill Cooldown and Fusion Skill Power rather than focusing on raw gun critical hits to ensure near-infinite uptime on your speed boosts. Down in the Sewer area near the train