3/3 Upgrades (Fortanono's Take)

This is my take on 3/3 Upgrades. It is balanced by the fact that the upgrade you buy second is nerfed to make for a tower about as powerful as a 4/4. Whichever side is not nerfed will be labeled with a "3+" rather than a "3". For example, a 3/2 will be upgraded to a 3+/3, and a 2/3 will be upgraded with a 3/3+. Once you get a 3/3 tower you can't upgrade it to either Tier 4 upgrade.

Dart Monkey

 * 3+/3 (Multi Shot): Works like the normal Triple Spike-O-Pult.
 * 3/3+ (Spike Flinger): Throws a volley of 3 spike balls with less popping power but a wider area of effect due to them being thrown like Triple Darts.

Tack Shooter

 * 3+/3 (Mixed Volley): Shoots 8 Blades and 8 Tacks.
 * 3/3+ (Blade Sprayer): Shoots 12 Blades.

Sniper Monkey

 * 3+/3 (Mon-K47): Pops 18 layers and fires slightly faster.
 * 3/3+ (Fully Auto Rifle): Pops 12 layers and fires as fast as a Semi-Automatic Rifle.

Boomerang Thrower

 * 3+/3 (Bionic Ricochet): Shoots ricochet glaives slightly faster than normal.
 * 3/3+ (Bag of Tricks): Throws a Ricochet Glaive every 5 shots, but fires as fast as a Bionic Boomer.

Ninja Monkey

 * 3+/3 (Flash Volley): Throws a Flash Bomb surrounded by 2 Shurikens every shot.
 * 3/3+ (Double Flash): Sometimes throws 2 Flash Bombs, but usually throws 2 Shurikens.

Bomb Tower

 * 3+/3 (Cluster Mauler): Cluster bombs where the central bomb does extra damage to MOAB-class.
 * 3/3'+ (MOAB 'Cluster): Only throws 4 bombs out after the central bomb in an X shape, but they all do extra damage to MOAB-classes.

Ice Tower

 * 3+/3 (Blizzard): No Arctic Wind effect. Instead, bloons will release an aura of slowness around them if popped while frozen by this tower.
 * 3/3+ (Arctic Shards): Basically Arctic Wind/Ice Shards.

Glue Gunner

 * 3+/3 (Bloon Disentigrator): Shoots slower than a Glue Hose, but pops as fast as Dissolver glue.
 * 3/3+ (Dissolver Hose): Pops bloons slower but shoots as fast as a Glue Hose.

Monkey Buccaneer

 * 3+/3 (Battleship): Shoots bombs independently and much slower, but the darts firs as fast as a Destroyer.
 * 3/3'+ ('Nautical Unit): Inspired by the BTD4 upgrade to the Buccaneer. Shoots bombs and darts rapidly much like a Spectre, but slower than a Destroyer.

Monkey Ace

 * 3+/3 (Target Storm): Shoots out 12 Neva-Miss darts.
 * 3/3+ (Operation Neva-Miss): Shoots out 8 regular darts and 16 Neva-Miss ones.

Super Monkey

 * 3+/3 (Moon God): Shoots out silver Sun God-style plasma from one eye and regular Super Monkey Plasma (albeit silver) from the other.
 * 3/3+ (Solar Powered): Shoots out a group of 2 sunbeams from both cannons.

Monkey Apprentice
More to come!
 * 3+/3 (Gust Breath): Shoots a stream of wind that pops and blows away bloons.
 * 3/3+ (Sunstorm): Basically a 3/3 Apprentice that shoots tornados and dragon breath, but the tornadoes are deep red.