The Tomb Raiser Zombies and Buckthead Mummies are pretty tough, plus, Flag Mummy Zombie can heal them, so the player needs to upgrade their plants.
Upgrade your plants' level by replaying previous levels. Then upgrade them more with Puzzle Pieces and the Oven in your house.
Drag as many plants as you can onto the lawn. Use other users' plants to have even more power. Make sure to have your attack as strong as possible to defeat the three front zombies quickly. It is recommended to put high-health plants at the back to prevent Tomb Raiser Zombie's skill from affecting your defenses.