I adapted this build from Buschkopf in order to make this work with my level 83 app with meh gear.
Hint 1: This is on the ground, not on the catwalk above. I usually upgrade this Buff beam first all the way before moving to my other beams.
Hint 2: Typical minion wall with 4 archers with 1 spider and 1 mage stacked, I use a 4DU Buff beam and a 1DU reflect, I have trouble keeping this one alive on the first round or two so I level up the beam to full and them the mage to full I usually level this beam 2nd