The bomb tower has an upgrade that does 10 times more damage to MOAB class bloons (MOAB mauler). It's not clear how many hits from that will pop a ZOMG.
Also we have the Cripple MOAB upgrade for the sniper. Again, I do not know how many hits from that will pop a ZOMG.
Some say that a Dragon's Breath apprentices are good against it. If so, how? Does that do extra damage against ZOMGs? What?
Also, the Sun God may be good against ZOMGs, but why?
I notice that Rays of Doom are good against MOABs, but not that good against unclustered ZOMGs.