The player is given a decent selection of plants to defeat the zombie horde. Sun-shroom will work great to produce sun, as well as using Sun Bean and Grave Buster (on Tombstones with sun in them). Fume-shroom and Hypno-shroom are the only offensive plants given. These can be difficult to work with, but the player should get at least two columns of Fume-shroom, along with a column of Wall-nuts. The key to winning is using Hypno-shroom strategically, namely on Knight Zombies and Buckethead Peasants. Other than that, the player should use Grave Buster well to avoid dangerous Necromancy attacks.
The small number next to the zombie icon means that zombie will always appear in that lane, with 1 being the topmost lane and 5 being the bottommost one.
First plant few Sun-shrooms as you do regularly. Then plant Grave Busters on tombstones to remove them and make the level easier. Then plant Fume-shrooms to defeat typical zombies.
Some of the hard zombies such as Buckethead and Knight Zombies appear, you do not need to worry, better to stop them using Sun Bean's and Hypno-shrooms. Hypno-shrooms are useful to return back the hard zombies.
Plant one column of Wall-nut and Hypno-shrooms. Then use Plant Foods only to Fume-shrooms (not other plants). There you go, the level is easy!