Ive found the FAQ but i dont understand it very well.
When you keep a 9 lvl gap between you lvl and you highest mastery, and then kill the same mob (usualy bandit archers) for a very long time, saving up SP. This usualy includes some de-lvling.

(i dont speak englisH)
Can u explain it? I see people talking about doing that fot 12k and 4x,8x or something like that. im on lvl 20, is it possible to do this?