I recommend doing this on Hardcore Mode, but ONLY during the very beginning of the game, otherwise, your whole progress will reset to 0%. You'll have 1 life on Hardcore Mode, so go to the fire logs near the entrance of the hub and kamikaze to get a game over.
You'll also get the achievement for dying in the hub and once you return to your Hardcore Mode save, the game will give you all the Rainbow Scales for free, extending your life bar, which will be very useful for the Hardcore Mode run and it will give you the achievement for getting all Rainbow Scales.