Throughout the stage, increasingly strong Zombie enemies are sent out from the enemy base, starting with Znache and ending with terrifyingly strong Zories. Kory appears when the base is hit.
Sniper the Cat power up can shoot the Zorys, causing them to not burrow. A hypermaxed Manic Flying is definitely a valuable asset in this level, also try to stack Manic Macho Legs to clear peons to allow Sniper the Cat to hit powerful zombie enemies.
You can also clear this stage by spamming units with decent damage and time between attacks (Like Kasa Jizo or Baby Gao).By stacking these units,you'll deal enough damage to knock back zombies when they are about to burrow,making them to not burrow.Also,they will deal a lot of damage to kory,reducing his health.A strong uber is recommended to take out the kory quickly in case he plows through your defense and reaches your base.
There is a time limit in this stage, at 3 minutes all zombie enemies (except zoge) will stop spawning, giving you a chance to fight kory without having to worry as much. This is probably the best way to beat the level on 2/3 stars as well, unless you have the ubers to deal with everything.