Upgrades

ABOUT
Upgrades are the main way to power up towers as of update 1.7, replacing forms. Updates are exactly what you expect, stat upgrades and design changes. Sometimes, they only upgrade a certain amount such as Marksman, never upgrading all of them, but always half or a few with each one. Some towers have unique stats such as Bombarder with Exclusion and Splash Radius.

Costs
Upgrade costs have a general pattern - Level 2 is approximately 1/2 to 5/6 of the tower's base price. Afterwards, the costs are generally anywhere between 2x to 5x as much as the previous one. Once you hit the level 7 upgrades though, those are usually 6x to 15x as expensive as the previous upgrade.

Effects
Upgrading can yield several effects, upon upgrading, but it can also delete effects. For more in-depth information on stat types including ones spawned with, read the link, stat types. The following are those

Addable Effects upon Upgrading

 * Burst
 * Burst CD
 * Stun
 * Paralyze
 * Shredding Bullets/SB

Removable Effects upon Upgrading

 * Burst
 * Burst CD
 * Armor Piercing