User blog comment:StarryStar34/BTD4 Idea 1: Add the ZOMG/@comment-1785597-20120528163111

B.F.Bs in BTD4 already cause lag in large numbers, plus they're harder to pop compared to in BTD5. At round 250 in BTD4, there are 999 B.F.Bs. In BTD5 that could probably be handled, but having even 100 Z.O.M.Gs would probably freeze the game.

The reason I think that the Z.O.M.G. isn't added in BTD4 is because of the limited upgrades. Same reason why the B.F.B isn't in BTD3 or that the M.O.A.B isn't in BTD 2.