When you stand under (or above) another platform where you can see a bunch of monster (mobs), and its open for you to use far range shot, press shift+ attack move you want, this make you using your skill from the upper (or lower) platform, without actually encounter mobs. This can be done with most far range attacks (esspecially alkemis's skill).

The pre mission done can be easily done by using doublycate glitch: play one character throught thestory easy mode, double up the mssion item, then put it in shared stash. then create another one, and take the mission item out, and give it to the mission giver, instance item! (remember NOT to pick up the real mission item in tha second char story, or you can NEVER get rid of it).