After 5 months of the 'Metal Slime' dungeon or better known as the level 20 glitch, I finally levelled up to level 21 today. For some it went quicker but I'm not that hardcore. At least I got there in the end.

I think there's another glitch around level 64 that takes ages to get through. I'd say it's going to take me a while before I see that one...