Tiers

Tier 1: Level 15
Upon reaching Level 15, the player may select one of these Tier 1 specializations.

Twin: Tier 1 Class upgrade that results in gaining an extra barrel next to the existing one. The bullet damage also decreases, and the spread is slightly bigger.

Flank Guard: Tier 1 Class upgrade that results in gaining another barrel on the side opposite to the existing one. It alternates between shooting forward and backward. The smaller flank barrel fires at half the rate of the normal one.

Machine Gun: Tier 1 Class upgrade that results in an improved rate of fire, and a slight spread to the shots. Like the Twin Shot, its bullet damage also passively decreases.

Sniper: Tier 1 Class upgrade that slightly increases the player's field of view and increases bullet speed/penetration at the cost of drastically decreasing reload time.

Tier 2: Level 30
Upon reaching Level 30, the player may select one of these Tier 2 specializations.

Twin Upgrades
Triple Shot: A triple barreled gun, but each turret is 45 degrees apart from the last, forming a wide spread that has little focus of fire. Can upgrade to Triplet or Penta Shot at Level 45.

Twin Flank: Will add two barrels to the back, and act like the Flank Guard above, respectively, but with two barrels on each side. Can upgrade to the Octo Tank or Triple Twin at Level 45.

Quad Tank: Often helpful for farming and hitting multiple enemies, but hard to aim with and has easily exploitable holes in its defense. Each turret is spaced out at 90 degree angles, making it more like the flank guard than the twin. Can upgrade to Octo Tank at Level 45.

Machine Gun Upgrades
Sprayer: The sprayer has an extra rectangular cannon added similar to the Hunter. Its RoV is increased, while the bullet damage is slightly decreased, but its hail of bullet might be every tank's thread to against. Is even slower than the Machine Gun, but has even more spray and bullets fired at a time. Extremely good at swarming enemies like Overseers (with high Bullet Damage & Penetration), but weak against other bullet spammers and Sprayers. Good at helping to capture Dominators. Only tank in game that is unable to upgrade at Level 45 along with the Gunner.

Gunner: The Gunner is an upgrade from the Machine Gun. The Gunner gets 4 cannons, each relatively small, and so are the bullets it shoots. The Gunner's bullet damage and penetration are passively decreased, but the bullet speed and reload increases a good amount. This allows for hard-to-escape bullet storms that can overwhelm and destroy other tanks with ease. Only tank in game that is unable to upgrade at Level 45 along with the Sprayer.

Destroyer: A long-range cannon that fires extremely slowly, but packs a punch harder than two cement trucks if you play your Skill Points right. The gun has such a forceful shot, the recoil sends you flying fast back a great distance. Damage and Health are passively improved with the upgrade. Can upgrade to Hybrid at Level 45. Quick tip: If you are going to use this class and you are trying to move around, shoot behind you to move faster in the other direction.

Sniper Upgrades
Assassin: Increases field of vision, damage and bullet speed further. Simply an improved Sniper. Can upgrade to Stalker or Ranger at Level 45.

Overseer: Instead of firing bullets, the Overseer summons controllable Red Triangles called drones that follow your mouse when you hold left click (or pressing E to autofire), allowing you to swarm enemies with a horde of minions, and you can right click to have them spread away from your mouse. The triangles will automatically attack any polygons close, however. The overseer can have a max of 8 Triangles. When not moving, the Triangles will circle around you forming a pseudo-shield. Reload helps spawn minions faster when not at max capacity. Bullet penetration and bullet speed turns into drone health and drone speed. Can upgrade to Necromancer, Manager, or Overlord at Level 45.

Hunter: The Hunter shoots a bullet, followed by a smaller bullet, each one being shoot out of a specific barrel. The Hunter seems to add some extra damage and penetration, but shoots very slowly. Can upgrade to X Hunter at Level 45. Note: It is the class that was most changed during the constant updates, it was nerfed right after it was released (now shooting a burst of 7 mini bullets) and later buffed to its original firing concept.

Flank Guard Upgrades
Twin Flank: Think of the regular Flank Guard, but with twice as many barrels. There are 2 in front, and 2 behind your tank. Can upgrade into the Octo Tank or Triple Twin at Level 45. Also, the back guns are now exactly the same size as the front ones.

Quad Tank: Imagine the Flank Guard, but double the barrels, one on all four sides shooting directly, often helpful for farming and hitting multiple enemies, but hard to aim with and has easily exploitable holes in its defense. Can upgrade to Octo Tank at Level 45. Not recommended to be using, as mentioned above, very exploitable weaknesses that are easy to take advantage of.

Tri-Angle: Think of a regular tank with 2 barrels at the back forming, as the name implies, a triangle. The barrels at the back give it a decent speed boost when going forward, while providing a possible bullet shield on the front. Great for chasing and/or avoiding tanks, as it is the fastest tank in the game.

Tier 3: Level 45
Every class except the Gunner and Sprayer may upgrade to these Tier 3 specializations upon reaching Level 45.

Twin Flank Upgrades
Octo Tank: Upgraded from Twin Flank and Quad Tank. Fires in all eight normally used directions (i.e the cardinals and diagonals).

Triple Twin: An upgrade from Twin Flank that now has three twin barrels and is consistently seen at the top of the leader board. It's got more bullet concentration but a bit of more vulnerable than Octo Tank.

Quad Tank Upgrade
Octo Tank: Upgraded from Twin Flank and Quad Tank. Fires in all eight normally used directions (i.e the cardinals and diagonals).

Triple Shot Upgrades
Triplet: An upgrade from Triple Shot. A triple barreled tank, that focuses fire in one direction. Looks like original twin shot, but has a longer gun between the two outer guns. The bullet damage will decrease a bit more. Greatest DPS frontal power.

Penta Shot: An upgrade from Triple Shot. Shoots five bullets evenly spread out in a more manageable angle than the Triple Shot. With a passively higher penetration, nothing can reach you. Also, retreating is easy because there is great recoil when firing.

Overseer Upgrades
Overlord: An upgrade to the Overseer, the Overlord can summon the same amount of minions but spawns them faster. Other than that, nothing is new. This and the Necromancer also have a secondary attack used by right-clicking that send all minions traveling away from your mouse.

Necromancer: An upgrade from the Overseer. Upon touching or killing a Yellow Square, it becomes your minion, and you can use it to quickly amass a huge army of up to 30 squares. Be wary however, never enter the Pentagon Nest, as you will run out of Squares and become vulnerable quickly.

Manager: An upgrade from the Overseer. This is a mixture of Overseer and Stalker features, which has only one of Overseer's barrel instead of two, and also has the ability to go invisible like Stalker does. As a note your minions will not go invisible with you, and if not directed, will circle around you, but you can move them and stay invisible as long you don't move. Great for camping unnoticed.

Assassin Upgrades
Stalker: An upgrade from the Assassin. This upgrade further increases your range and field of view. When you are still you become invisible. Stealth is broken when you shoot or move. This is the best class if you like the classic sniper feel with extra benefits. However the damage seems to be decreased but this is not confirmed.

Ranger: An upgrade from the Assassin. It increases your range and field of view even more. That's the only feature to the class (so far). Great for dodging and predicting bullet patterns.

Tri-Angle Upgrades
Fighter: An upgrade from the Tri-Angle. This upgrade allows you to have 2 extra barrels at the sides of your tank. Also passively increases bullet damage. Frontal cannon still does the most damage, but crowd control is a nice addition.

Booster: An upgrade from the Tri-Angle. This upgrade adds 2 extra barrels, 1 additional barrel under each barrel already on the back of your tank. Notice that with full reload, you don't even need to use the arrow keys or 'WASD' keys to move anymore as it has a very noticeable amount of force going from the back. Avoid going for Alpha pentagons as you may be pushed towards it.

Destroyer Upgrade
Hybrid: An upgrade from the Destroyer. This upgrade adds extra backward barrel which is similar to the one from an Overseer class, can summon up to 2 drones. The drones cannot be controlled like they are as an Overseer class, instead they will destroy any polygons which are nearby, or try to homing the nearest-to-be-seen enemy tank. Otherwise they will go around you as a pseudo shield.

Hunter Upgrade
X Hunter: An upgrade from the Hunter. This upgrade adds an extra barrel to the exist 2 barrels that the Hunter has. It shoots a large bullet followed by a medium-sized bullet and a small bullet.

Predator: An upgrade from the Hunter. This upgrade adds an ability to concentrate only at the cursor's present aiming point when holding Right click or Shift key. Note that the concentrating screen DOES NOT move when the tank moves, and the other sides' concentration is reduced, therefore it might be tricky and dangerous for you while doing the aiming since your tank can be off-screen.