Story-related achievement; cannot be missed.
Underworld is the third world of the game and is made of 5 levels, with the last being just a boss fight against the Kings of the Underworld.
For those that need help with anything in the levels from layout to coins/scrolls, here's a playlist for each level.
https://www.youtube.com/playlist?list=PLyx3ruPOCg3_iBrN7cdJK...