I don't know, just got to level 31 and lost 16 strong mutilated zombies. (against robots)
All I can say is they were all zombarians. So I'm guessing you might need a good variety.
I ll try again in the next day or two and let you know how I get on.

It's really difficult, Ive tried different combination of powerful zombies, I still can't
beat the robot.... Who can help?

When the big robots face starts to glow tap it repeatedly

yes try a zombomkin

All your zombies need to be mutants and masters, send in some zombarians and party zombies
first, the mix up the zombielocks and robo zombies, I always have two zombee's and send
them in last. As soon as you see the eyes of the big robot light up tap on it repeatedly.

Beating robot is easier.. sent in Zombarians, with 2-3 zombee. Tap the eyes of Big Robot

To beat aliens, I figure the best is to have 3x party zombies, they will take all the
beatings and defennd the rest from the Alien King. I always have 5-6 zombee to resurrect
the dead Pary Zombie. This works everytime, win without any lost.

6 robozombies 6 zombielocks 3 zombee 1 partyzombie mutated with thee 5 best mutations all
master. can beat them before 1:30 without losing or ressurecting any zombies. Start with
party followed by a zombee.

zombees, zombrutes, zombarians, zombots and party zombies are good

zombielocks is good too