Have you considered that you are sharing in Crazy David's madness? There is no zombie outbreak threatening you. You are not using plants to defend your home. The zombies and I are normal people, simply trying to help you.
Melon-pults and Winter Melons are all-powerful plants that the player can have in their arsenal. However, they are limited, hence only a small of number of them are given so that Zombot War Wagon is not defeated easily. Recall that Melon-pult and Winter Melon have three-by-three radius of splash damage.
Zombot War Wagon not only has a lot of health, but also has a missile attack similar to Zombot Sphinx-inator's. These can target up to three of any player's plants, leaving them susceptible to upcoming zombies. It will frequently use this tactic.
At the second phase, it can call hardened zombies such as Poncho Zombie and Wild West Gargantuar, allowing itself to wait and use its infamous charge and assault.
Place one set of Pea Pods on the fourth column since it has a minecart on it and one Winter Melon on the second column as well since it has a Mine Cart also. That way, you can move both Winter Melon and Pea Pod in order to damage the Zombot and its zombies. For the case of Winter Melon, you can use this to disarm Prospector Zombie's dynamite.
Alternately, you can also place Pea Pods on two Mine Carts but keep one Melon-pult as a reserve . Winter Melons are on second and fourth column while Melon-pults are placed in first, third, and fifth columns.
Another alternative is placing both Winter Melons on both minecarts, as in such a situation they can be moved wherever needed and deal slowdown to zombies in almost any places.
When it is about to attack with its missile barrage, sometimes, it will target the one that is in the minecart, if this ever happens move the plant away from the target range. However, it will also target the other plants that are not in the cart as well.
Do not forget to replace lost high priority plants immediately. They are the key on stopping zombies.
When the Zombot is about to do its infamous charge and assault attack, feed either the Melon-pult or the Winter Melon with a Plant Food. This will stun Dr. Zomboss immediately. You can also do this to the Split Peas but it is not advised because Dr. Zomboss will use his henchmen as a shield. Keep in mind that doing this to Lightning Reed (unless there is no zombies on the screen except the Zombot) is a very bad idea, as it targets a random zombie on-screen.
While using a Winter Melon's Plant Food effect works most of the time to stop his charge attack, sometimes, especially in stage three of the health bar of the Zombot, it is unfazed by the catapult plant's Plant Food upgrade at all when he is doing his charge and will proceed to destroy plants from both lanes anyway. You have no idea when this will happen so be prepared.
Lightning Reed's Plant Food effect can stop the Zombot War Wagon even if the cloud does not target it, as Lightning Reed becomes briefly invincible for a very short period of time, and the Zombot stops charging and is stunned if it hits an invincible plant.
If you timed it correctly Split Pea's plant food ability can do a lot of damage if you plant them in the area where the zombot is.
Place the Tall-nuts at the third column to prevent the Zombie Bull Riders from wrecking your hindmost part of your lawn.
Alternately, you can place Lightning Reeds in the third column. Tall-nuts go to seventh column where Dr. Zomboss calls his henchmen. It makes a perfect way to stall summoned zombies especially Chicken Wrangler Zombies.
Melon-pults and Winter Melons go always at the back.
Just like its previous variations of Zombot, it has three tiers or phases.
Tier one - Cowboy Zombies, Conehead Cowboys, Pianist Zombies, and Prospector Zombies are only summoned. Prioritize the Pianist Zombies before it wreaks havoc along with its dancers, as it does not get instantly killed by the Chili Bean in the latest version. A Winter Melon and a Pea Pod with at least three heads will do it justice. Split Peas are at your disposal if ever Prospectors will fly over to the left edge. These are the only zombies that are summoned until one-third of its health is gone.
Tier two - Poncho Zombies, Zombie Bull Riders, and Wild West Gargantuars are already summoned and Pianist Zombies and Prosepector Zombies are no longer summoned. At this moment, start increasing your defenses more. If ever a Wild West Gargantuar is summoned, feed the Pea Pod with Plant Food but first deal enough damage before doing so, that way it will die without ever getting the chance to throw the Bull Rider. Otherwise, the Chili Bean.
Sometimes, three to four of Poncho Zombies, two to five of Conehead Cowboys, two to four of Cowboy Zombies, and two of Zombie Bull Riders alone are summoned at this stage. That is where the Chili Bean strategy will take over.
Tier three - Buckethead Cowboys and Chicken Wrangler Zombies are finally summoned. Place the Lightning Reeds already if you have not because Zombie Chickens will devastate your rows if not. Two to four of Ponchos with three to six of Bucketheads and two to three of Chicken Wranglers are summoned at this part (this also include the Cowboy Zombies and Conehead Cowboys). If ever things get rough, use Plant Food on Winter Melon to slow them down. You can place Tall-nuts at where Dr. Zomboss calls his henchmen to force Chicken Wrangler Zombies to break their bailing wires, releasing Zombie Chickens. This can also save most of your time in increasing your defense parameters. Remember that even though they are rare, Wild West Gargantuars may be summoned.
Always bear in mind that always stall the zombie with the highest level of threat.
This is one of the Zomboss Battles that use every plant in its world.
Like the battle with the Zombot Plank Walker, some plants are only received numerically. Winter Melons (due to it being one of the powerful plants in the game) can only exist two at a time (if one dies, another one will appear in the conveyor belt to replace it). In the same way, only two Chili Beans can exist at a time. Also, only five Tall-nuts and four Melon-pults can exist at a time.