User blog comment:Sam Wang/BTD5 - Tips For Reaching High Rounds/@comment-3153244-20120808070404/@comment-3153244-20120808080801

Rays of Doom haven't been so effective since the nerf. I generally use RoDs on Monkey Lane Apopalypse for XP farming. I usually don't reach such high rounds, mainly because I have to play each day's Daily Challenge for the achievement "Driven". I read somewhere that the frags of MOAB Maulers also do a lot of damage...not sure of the numbers though.