Cant shoot 20 helghast with bolt its hard because barely none of them are standing close to a wall

this one isnt all that hard. Juts, as soon as you get the blot gun in the Suljeva level, use it a lot. Try to not just fire anytime you see an enemy. Instead, try to line them up against a wall or a box or whatever and then fire so they get stuck. Remember that if you kill them with it and they don't get stuck, it doesn't count. The pushback his pretty strong so the enemies can stand a good distance from a wall or what ever and still get nailed up. And lastly, there nothing wrong with playing on super easy and dieing on purpose to do the part over and over again ;)