The first world I thought of has to do with the roman coliseum Basically the Romans got infected and are now zombies and the zombies are

Roman zombie which is the basic zombie in Rome

Roman cone head zombie which is the cone head zombie in Rome

Roman bucket head zombie which is the bucket head zombie in Rome

Roman flag zombie carries a flag which is like the regular flag zombie only in Rome

Centaur zombie kick plants in front of it but gets rid of them unlike mecha football zombie

Roman warrior zombie take 5 hits from scardy shroom before dying no other plant can kill it if it gets shot it becomes more and more stronger it can be stronger than any zomboss

Pompeiigranate shoots fire is based on a pomegranate

Scardy shroom long range shooter hides when zombies come close and can die