In case you didn't understand what the rap meant, here is the meaning.
Oh Peashooter. You sayin that you are famous?!
(Peashooter has appeared in every PVZ game)
HA- HAH. You're hearing it.. You're fearing it.. You're feeling it.. You are a loser. A failure!
(Peashooter is very universally disliked.)
You're worse than a dozer!
Shoot peas?! HA. Plants can shoot COBS with EASE!
(Cob cannons are more powerful than Peashooter in both PVZ and PVZ:GW)
Come on, peashootie. You know that.. You are just a small inpopular loodlie!
Yo I'm about to call yo brother. Repeater.
Cause he's much better than you, you rodler.
(Peashooter is often replaced by Repeater early in the game.
And your sunny girlfriend Sunflower, she hates you.
(As said, Peashooter is very universally disliked.)
You must be in a sadshower, like tofu.
Because right now.. MasterNinja is stealing this race! I'll go apesh*t on your butt! Restructure your face!
(His face looks like a cannon, so MN is restructuring it to a real mouth)
Do you think you're superior?
(Peashooter thinks that MasterNinja321 is inferior as compared to him)
Well, let's go and show this german blover who's better.
(Peashooter is not just going to say he is better than MasterNinja321. He will prove that he is better through their raps)
I'm a soldier. You're like a lady.
(Peashooter was featured in PVZ:GW where as Blover and his variants did not appear in that game. Peashooter is therefore implying that Blover is weak plant who could not stand up against the front line in a war)
For I have been through a thousand wars.
(Peashooter has appeared in a lot of battles in PVZ:GW)
You think you have seen a battle? Just wait till I fire.
(Peashooter thinks that if MasterNinja321 has fought a lot of zombies who just shuffles forward, he should have seen a battle in GW)
I'm smoking up this room, gunning you down, till you tire.
(This is reference to either Peashooter's Chilli Bean Bomb or the Zombie Stink Cloud)
For I'm the real plant. You're more like a recruit.
(Peashooter has appeared in everyone PVZ game since 2009 where as for MasterNinja321, his advatar was only born a few months after 2014. this is also referencing his play in PVZ:GW)
You only knew how blow wind.
(Four-leaf Blover's attack really blows wind. Peashooter is disappointed to know how can wind deal any damage since peas will definitely injure zombies but wind will only make the zombies feel relaxed)
My weapons hurt more than your windblower did.
(He thinks that a fan will not deal any damage while his pea shots can damage them)
And so what? No one has ever ever heard of you and your eyes.
(peashooter has appeared in all PVZ games while Four-leaf Blover has only appeared in one PVZ game, PVZ: All-stars. He also does not like how Four-leaf Blover looks)
Heh. So yeah. I am german. So how many lanuages do you know?
I know MANY. You only know ONE, derpy pow.
(He was never seen speaking any lanuage outside English/game lanuage, while MN is able to speak English, German and Hungarian.)
Think you can hurt me with puny raps? Never. Ever. Try to do so
I'm going to stuff you in a lot of many wraps! I'll make your head spin.
(MN thinks his rhymes are very weak, and is trying to make him dizzy (head spin) from his raps.)
When it comes to rhymes... I'm stinging you like a shark fin.
Me only know how to blow wind?! HA. I CAN BEND AIR!
(Four-Leaf Blovers can't just blow wind, but can do many stuff with Air, as seen in PvZAS.)
You can just find.. That you suck.
Now get out of my way and duck. I'll say this once, Peashootie. I hope it's understood.
Get right back in your plant car.. and get the F*CK outta my neighborhood.
(The irony here is that they DEFEND neighborhoods.)
You think you can be pro? I suggest you try bungee-jumping.
(This is a possible reference to survival:endless or the fact that despite being in midair, Blover could not blow them away)
You're downgrade can't even deal with a king.
(Four-leaf Blover's downgrade, Blover, cannot blow away Zombie King while he is falling down in midair, even though it was mentioned that Blover can blow away all flying zombies)
And what happened to you?
(Peashooter ask MasterNinja321 what happened to him, possibly in a mocking way)
Popcap decided to nerf you. Made you unable to strike immediately.
(In version 2.1 of PVZ2, Popcap made Blover's ability work after a while. Before that, the moment he was planted, Blover would instantly kill all flying zombies when he gets planted)
My plant food ability can gun down greatly.
(Peashooter's plant food ability is to become a Gatling Pea who shoots a lot of peas)
Your cousin wouldn't even wanna face those f**king zombies.
(This is a reference to Shamrock, a cousin of For-leaf Blover since both of them are clovers)
And being in rock star? More like being a c**t thump.
(This is a reference to Shamrockstar, another clover. In this case, Peashooter thinks that rock stars are bad influence)
For I have seen the worst but can remain here.
(Although PVZA closed down, peashooter continues to live on in other PVZ games. As for the two clovers, they currently do not exist in other PVZ games.)