6-5 Omega is the last and by far the most difficult level of The End light world (not counting the final boss). It often takes as long to complete this level as it took to complete the previous four levels combined, and consists of a series of buzzsaw-filled floating islands, increasing in difficulty. It's dark world counterpart is '6-5X No Quarter'. The light world level, like 6-2, has no.
Meat Boy
When it comes to how difficult a level is in super meat boy there are usually several aspects to determine how tough a level is. Some of the aspects include is how long the level is, the level having lots of obstacles, if the level has a light world or dark world counterpart or how fast paced the level is. Some of the hardest levels in the game have a focus on one or a combination of these aspects. For example The Kid from I wanna be the Guy warp zone is a hard level because of how long it goes on for and having to go back the start of the level if you decide to exit it. The Cotton Alley levels tend be difficult by filling the levels full of various obstacles like buzz saws, spikes on the walls, disappearing and reappearing blocks. Having to collect any bandages can make any level more challenging however once they are collected the difficulty can go down somewhat. Difficulty of a level can also be affected by playing as characters that are not Meat Boy.
Super Meat Boy Game
Hard levels
7-20, 7-20 X, 6-5 Omega, 7-19X XOXO, 5-17X Millenium, 5-18X Stain, 5-20X Quietus, 7-18X They Bite, 4-16X Starless