Level 4-13 was a bonus level, and the thirteenth Fog level in Plants vs. Zombies: Journey to the West. The player had to pay 20 gems to gain access to this level. To complete the level, the player had to not lose more than 5 plants.
There were only four columns visible for the player at the start of the level. It could have been hard for the player to determine which lane zombies are spawning on at the beginning of the level.
This could have made the player fail the objective easily.
Plant Sun-shrooms and Puff-shrooms for an easy defense at first.
Use the same strategy in Level 4-8, but use the Cattail to pop Balloon Zombies (if you bought it) instead of Cactus. Cattails are more efficient in Pool or Fog levels. Try to plant at least four Cattails in this level for it to be really easy.
Use Planterns or Blovers (if you do not have Cattail, as stated before) if you want to see through the fog. Just remember that seeing through the fog is a luxury, as it is not required.
Use the Plant Hero to help you defeating tough zombies such as Buckethead Zombies or Pogo Zombies.