We must protect this houseG 5

We must protect this house G5:
Complete 10 waves without allowing any damage to the Gate

This can easily be done in the first 10 waves of the game. Simply focus on attacking the zombies with your own characters attacks/special attacks, and also spamming allies to aid you/slow down the zombies advance. Basically just kill the zombies before they even get close to your gate, which in the early levels, should be no issue.