Since it is the first level of I, Zombie, it is not too difficult. Use cheap zombies like the normal Zombie to get sun by eating Sunflowers. Then, once you have enough sun, use Buckethead Zombies or Football Zombies in lanes with more Peashooters. Be careful to not use strong zombies such as Buckethead Zombies or Football Zombies in lanes with Squash, or else they will be wasted. Use the normal Zombie to get rid of them.
Where the Sun Don't Shine
The achievementWhere the Sun Don't Shine requires a bit of skill to get. You need to balance out your zombies and Buckethead Zombies. Try not to use Football Zombies if possible. Whenever there is a Squash, use a Zombie, unless the Squash is in the back of a tight defense, in that case, use Buckethead Zombies. And remember, only use normal zombies to eat the brains if the lane is free of plants that could kill them. You effectively have a budget of 950 sun, because if you spend more than that, you will finish with less than 1000 sun. Try to spend a maximum of 175 sun per row.
