MT build FoWsc

hello after making a lot of runs ive finally mastered t2 in fowsc getting pretty sweet times. Now im movimg to the next role mt here
comes mu trouble ive seen the builds in gwpvx and ive got my brother to teach me but ive seen that in the gwpvx build there are two obtionals i know that unseen is better than AoE but how can i replace mb and waht with skill?

I would not suggest replacing Mental Block simply because with pugs spikes are slow and you are guaranteed to sit and tank rangers at some point. Without MB you'll have to either dodge back and forth or have really quick spikers or pop pcons, none of which are desirable imo. Also, forest is easier with MB. Mental Block is by no means needed, however, it does make things quicker unless you're A/P, which isn't practical in a pug environment.