The Sun and Moon

System Ten consists of levels 141 - 150 plus boss level X. Remember that there is no time limit for completing levels for this achievement, so take your time so you don't needlessly die over and over. 

System Ten has you making very precise movements on or through very small platforms and blocks, where there is basically no room for error. Some of the levels can look pretty intimidating at first. You just have to get used to moving only how much is required, so you don't hit spikes. Thankfully, the boss level (which is located up in System Nine) has no boss or dots and just rolls the credits upon getting to the top, so it's a nice calm ending to a very difficult system. 

Upon completing all 10 levels and boss level X, the achievement will unlock.