okay.. so small 360s are easy, big 180s are hard. 540s are a little harder to spin than 360s, and a lot harder to land. 720s are a lot harder to spin than 360s, and a lot harder to land. 180s are easier to spin than 1080s, but when done right are supposedly much harder to land. mutes are harder than safetys, because ski crossage defys physics as a whole. true tips are harder than true tails to some, but for others its the other way around. 720s and 900s can both take many years of practice unless your using 160s, which are much easier than 170, which are much easier than 180, ect. by the way, x grabs and double lui kangs push it to the limit in xxxtreme.