You can use a grenade to lunch yourself over the boss cage for example.
I think its considered an exploit because its not really suposed to be designed that way.

Emargwapo2x2 does it, he should be banned cuz its an exploit.
In my opinion

I have 2 skill points in blind hits and I can't downgrade :/
I don't really have anymore motivation to keep playing cause of that...

I accidentally upgraded blind hit in the warrior skills and now I cant downgrade it...
I suggest that you should be able to downgrade any skill already upgraded and it would give you the skill point back like it sometimes does.