Ok, this mission is pretty hard if you don't have a good group. So heres wat you can do u need atleast 2 monks and the rest can be warriors doesnt matter what your party is made of though.
Step 1: Get to the Ghost gate guarding a gate should have green exclamation mark over his head DO NOT TALK TO HIM!!!!
Step 2: Get your Whole group to go right next to the gate.
Step 3: Run at the gate have every1 do it
Step 4: It should have let all of you but one go through the gate make sure that person will not leave because they will be doing nothing for awhile and in order to return he must talk to the ghost
Step 5: Once every1 is through but the one there is another gate you must go through do the same thing as the first one again some1 must stay behind leaving only 4 people able to kill the stuff and get the crystals.
Step 6: Clear out the whole area get the crystals. Best if you got 2 monks and 2 warrior clearing place out does not matter though
Step 7: Once you got the crystal drop it next to the closed gate where the person left behind is. He picks it up and drops it on that side
Step 8: get the other crystals and give it to the person and they drop it on that side.
Step 9: Now the very first person left behind must talk to the ghost guy u go into cinematic now once thats over run pick up the crystals and deliver them to the guy and you win
Step 10: Mission has 30 minute timer and is kind of hard so this helps out alot
Have Fun!