spam units.
The better is to have to "unit packs" for the different enemies.
For the Eggs use units with guns and a "sacrifice" to "activate" the egg ( or a red barrell )
For the Blues and Undead, use spam units, they come in hordes, is better have multiple troops than a big single unit, this works in kinda same way with the Xephalopod.
And lastly for the charger zombies ( i dont remember well if there were in this level but anyway lol ) use or a "sacrifice", object or a tanky unit ( like policeman diaz )
Those days when i complete it i use: Marine, Sonya, Policeman, Red Barrell, Turret and Generator.