On level 7: Copter 1 has its damage type changed to Elemental, each rocket's AoE is increased by 25% and the attacks gain a napalm modifier. Napalm causes a 20% slow and 50% of the tower's attack damage as Elemental damage per second for 5 seconds.
On level 15: Copter 2 will change its machine-gun-missiles to a long ranged tesla coil, changing the damage type to Energy and increasing attack range to 2140. Furthermore its armor reduction base effect is increased to 50%, but the slow is decreased to 10%.
On level 25: Copter 3 will become a legendary Ghost Warrior. Ghost Warriors have an on-board teleportation device, allowing them to teleport behind targets every 5 seconds. Shooting delays the charging of the teleportation device.
Helicopter Zone
3 helicopters circle around the tower trying to stay within 1000 range of it. If there are targets in front of a helicopter, it will attack them dealing the tower's attack damage as Physical damage. Helicopters attack every 0.25 seconds with a barrage of 3 missiles spaced 250 range apart and exploding in 140 AoE. Damaged targets are slowed by 50% and their armor is reduced by 30% for 0.8 seconds. Not affected by attack speed.
Level Bonus: +0.4% armor reduction
Targeted Run
Copter 1 will teleport behind the target after a delay of 1 second.
Special Training 
Helicopter Zone 
Targeted Run 
