Upgrades, which are purchased from the Gun Dealer NPC, impact a player's Ultimate Tower. An Ultimate Tower starts at $1000 cost and upgrades from the Normal Tier 3 Tower. This is the only Tower which may be upgraded outside of a match. Every level upgraded in this fashion will increase the cost of the Ultimate Tower by $250.
Upgrades for the Ultimate Tower include Mechanical, Gun Powder, Barrel, and Shell upgrades.
The Mechanical Upgrade increases how often the Ultimate Tower fires.
The Gun Powder Upgrade increases how much damage the Ultimate Tower deals.
The Barrel Upgrade increases the max range of the Ultimate Tower.
The Shell Upgrade increases the splash radius of the Ultimate Tower.