User blog:Spike144/History of towers and their upgrades

Here is the list of the towers and their upgrades. Names of the towers and upgrades may be different in different BTD games. Color describes which BTD games is the tower or upgrade available in:
 * BTD1-BTD5
 * BTD2-BTD5
 * BTD3 & BTD5
 * BTD3, BTD4 & BTD5
 * BTD4 & BTD5
 * BTD5 only