Peashooter

The Peashooter is a Plants vs Zombies-themed tower. It costs $170 and pops 1/4 of a layer per shot (4 layers per shot to things that take more than 1 hit to pop). It fires at the same rate as a 0-0 Dart Monkey, but with 5% more range.

Repeater
Cost: $140

Description: Shoots two peas at once.

This upgrade is almost the exact same as the first upgrade on the second path of a Dart Monkey, but with the weaker projectile of the Pea. It also doesn't increase the popping strength of the projectile; it just adds another.

Hardened Peas
Cost: $155

Description: Peas now have coats that are twice as hard - increasing the damage along with the speed!

This upgrade is exactly what the description says; peas do double damage, but they are still stopped cold by the one bloon they hit. It also lets the peas travel faster; 20% faster. Oh, and they can damage frozen bloons now, too.

Frozen Peas
Cost: $620

Description: Increased water content in the peas lets them safely be frozen - it's also done automatically.

Basically, this makes peas act almost like the Ice Tower; they freeze any bloon they hit, except for Whites, MOAB-class bloons and Zebras, but they still take damage from the attack itself. The peas also gain a chilly, but weak, AoE effect; any bloon that is very close to the bloon that gets hit are slowed down.

Frozen Beam
Cost: $5200

Description: Frozen Beam Ability: Shoots near-absolute zero nitrogen in a beam at the bloons for 15 seconds.

This upgrade grants the mentioned ability; it fires a continuous, 250-pierce beam that pops 1 full layer off of any bloon, freezes bloons solid, and slows down ice-resistant bloons. The tower also fires 30% faster and has 10% more range.

Sharpshooter Pea
Cost: $325

Description: Specialized glasses let the Peashooter fire with greater range.

Range is boosted by 40%, and attack rate gets a 2.5% boost.

Threepeater
Cost: $1055

Description: Minor genetic mutations give the Peashooter two extra heads, tripling effectiveness.

The Peashooter gets a total of three heads. Each have slightly independant firing (head turn of 30 degrees), and it also fires 5% faster.

Burning Peas
Cost: $2000

Description: Special heat-tolerant pesticides let the Peashooter fire peas that are on fire.

This upgrade increases fire rate by 10%, makes the peas pop 2 layers by default, and permits popping of leads (as well as frozen bloons, but you probably have the Hardened Peas upgrade by now).

Super Rapid Fire
Cost: $9500

Description: Extreme training allows your Peashooter to fire at crazy speeds, maximizing total poppage.

Attack rate is boosted by 200%, and range is increased by 10%.

Trivia

 * This is the first tower based off of something from Plants vs. Zombies.
 * The first thing to reference Plants vs. Zombies is the T.M.A. Mk. III.