Glistening Lowland is one of the most easiest instances you can do. All you have to do it combine 2 of the smaller crystals and make them into a bigger one then take that crystal to the color it matches to. The pt. must do this 20 times to gain enough crystal energy to allow the Crystallized Demon to spawn. Once the boss spawns DONT HIT IT! Wait for someone to combine 2 smaller green crystals and make a bigger green crystal and push it into the boss. The party will now have a 3 minuet attack buff if and when that buff runs out you can make another green to get the buff again. Other crystals do things to the boss as well.
Green = Attack Buff
Red = reduced attack for boss
Blue = reduce defense for boss
Cyan= remove attack and defense stacks of buffs from the boss
Yellow= Stuns Boss
Purple= Reduces the healing effect the boss has
Once the boss is dead you will have 1 gem box if you are between lvl 40-59 you will earn 2 gem boxes if you are between lvl 60-80