The purpose of this guide is to break down all of the various towers and their item upgrades in Defense Grid 2.

Tower item upgrades are passively added and do not require a Boost Tower below them, or need to be activated in any way. As soon as you build a tower, it will have the upgrade you chose before the level started.

Currently being investigated.

Upgrades seem to be given randomly after winning a level, in single player, co-op or competitive multiplayer.

From dev Kaboom here
"Specific tower items are rewarded at random, so there is no set level or playthrough that will reward X item. However, there are things you can do to increase your chances of getting a higher quality item or just getting one in general. What map you're playing, what difficulty you're playing on, and how long you've been playing the mission are all factors in your chance of getting an item as well as its quality."

Chemical Tipped Bullets
01 "Chemical Tipped Bullets inflict an additional 20% damage over time as a substance slowly eats away at them."
02 "Chemical Tipped Bullets inflict an additional 40% damage over time as a substance slowly eats away at them."
03 "Chemical Tipped Bullets inflict an additional 60% damage over time as a substance slowly eats away at them."
04 "Chemical Tipped Bullets inflict an additional 80% damage over time as a substance slowly eats away at them."
05 "Chemical Tipped Bullets inflict an additional 100% damage over time as a substance slowly eats away at them."


Priority Target Strongest
01 "Makes strongest alien in range the highest priority target."
02 "Makes strongest alien in range the highest priority target and inflicts an additional 20% damage."
03 "Makes strongest alien in range the highest priority target and inflicts an additional 40% damage."
04 "Makes strongest alien in range the highest priority target and inflicts an additional 60% damage."
05 "Makes strongest alien in range the highest priority target and inflicts an additional 80% damage."

Scatter Shot
01 "Scatter Shot inflicts a 10 degree cone of fire on target area."
02 "Scatter Shot inflicts a 15 degree cone of fire on target area."
03 "Scatter Shot inflicts a 20 degree cone of fire on target area."
04 "Scatter Shot inflicts a 25 degree cone of fire on target area."
05 "Scatter Shot inflicts a 30 degree cone of fire on target area."

Shield Buster
01 "Shield Busters do an additional 20% bonus damage against shields."
02 "Shield Busters do an additional 40% bonus damage against shields."
03 "Shield Busters do an additional 60% bonus damage against shields."
04 "Shield Busters do an additional 80% bonus damage against shields."
05 "Shield Busters do an additional 100% bonus damage against shields."

Shield Piercing Rounds
01 "20% of damage from Shield Piercing Bullets penetrates shields and inflicts directly on alien."
02 "40% of damage from Shield Piercing Bullets penetrates shields and inflicts directly on alien."
03 "60% of damage from Shield Piercing Bullets penetrates shields and inflicts directly on alien."
04 "80% of damage from Shield Piercing Bullets penetrates shields and inflicts directly on alien."
05 "Shield Piercing Bullets completely bypass shields and inflicts damage directly to alien."

Tachyon Bullets
01 "Tachyon Bullets slow down targets temporarily."
02 "Tachyon Bullets slow down targets temporarily, and inflict an additional 15% damage."
03 "Tachyon Bullets slow down targets temporarily, and inflict an additional 30% damage."
04 "Tachyon Bullets slow down targets temporarily, and inflict an additional 45% damage."
05 "Tachyon Bullets slow down targets temporarily, and inflict an additional 60% damage."

Liquid Fire
01 "20% Increased damage over time as target burns for longer"
02 "40% Increased damage over time as target burns for longer"
03 "60% Increased damage over time as target burns for longer"
04 "80% Increased damage over time as target burns for longer"
05 "100% Increased damage over time as target burns for longer"

Concentrated Fire
01 "Intense heat inflicts 25% additional damage on target with a tighter cone of effect."
02 "Intense heat inflicts 50% additional damage on target with a tighter cone of effect."
03 "Intense heat inflicts 75% additional damage on target with a tighter cone of effect."
04 "Intense heat inflicts 100% additional damage on target with a tighter cone of effect."
05 "Intense heat inflicts 125% additional damage on target with a tighter cone of effect."

Priority Target Strongest
01 "Makes strongest alien in range the highest priority target."
02 "Makes strongest alien in range the highest priority target, and inflicts an additional 20% damage"
03 "Makes strongest alien in range the highest priority target, and inflicts an additional 40% damage"
04 "Makes strongest alien in range the highest priority target, and inflicts an additional 60% damage"
05 "Makes strongest alien in range the highest priority target, and inflicts an additional 80% damage"

Shield Eroder
01 "Shield eroding chemical does an additional 20% bonus damage against shields"
02 "Shield eroding chemical does an additional 40% bonus damage against shields"
03 "Shield eroding chemical does an additional 60% bonus damage against shields"
04 "Shield eroding chemical does an additional 80% bonus damage against shields"
05 "Shield eroding chemical does an additional 100% bonus damage against shields"

Torch Bearer
01 "Targets hit by flames set fire to any aliens that they come in contact with for an additional 20% damage."
02 "Targets take an additional 20% damage on impact, and set fire to aliens they contact for 20% damage."
03 "Targets take an additional 40% damage on impact, and set fire to aliens they contact for 20% damage."
04 "Targets take an additional 60% damage on impact, and set fire to aliens they contact for 20% damage."
05 "Targets take an additional 80% damage on impact, and set fire to aliens they contact for 20% damage."

Priority Target Strongest
01 "Makes strongest alien in range the highest priority target."
02 "Makes strongest alien in range the highest priority target and inflicts an additional 20% damage."
03 "Makes strongest alien in range the highest priority target and inflicts an additional 40% damage."
04 "Makes strongest alien in range the highest priority target and inflicts an additional 60% damage."
05 "Makes strongest alien in range the highest priority target and inflicts an additional 80% damage."

Shield Piercer
01 "20% of the Shield Piercing beam penetrates shields and inflicts damage directly to alien."
02 “40% of the Shield Piercing beam penetrates shields and inflicts damage directly to alien.”
03 “60% of the Shield Piercing beam penetrates shields and inflicts damage directly to alien.”
04 “80% of the Shield Piercing beam penetrates shields and inflicts damage directly to alien.”
05 "Shield Piercing beam completely bypasses shields and inflicts damage directly to aliens."

Shield Splitter
01 "This shield disrupting beam does an additional 20% bonus damage against shields."
02 "This shield disrupting beam does an additional 40% bonus damage against shields."
03 "This shield disrupting beam does an additional 60% bonus damage against shields."
04 "This shield disrupting beam does an additional 80% bonus damage against shields."
05 "This shield disrupting beam does an additional 100% bonus damage against shields."

Tachyon Beam
01 "Slows down targets while inflicting heat damage."
02 "Slows down targets while inflicting 15% additional heat damage."
03 "Slows down targets while inflicting 30% additional heat damage."
04 "Slows down targets while inflicting 45% additional heat damage."
05 "Slows down targets while inflicting 60% additional heat damage."

Wide Beam
01 "This area of effect beam inflicts a 10 degree cone of damage to target area."
02 "This area of effect beam inflicts a 15 degree cone of damage to target area."
03 "This area of effect beam inflicts a 20 degree cone of damage to target area."
04 "This area of effect beam inflicts a 25 degree cone of damage to target area."
05 "This area of effect beam inflicts a 30 degree cone of damage to target area."

Airburst Ordnance
01 "A cloud of shards is unleashed at the point of impact, inflicting 20% damage in a small radius."
02 "A cloud of shards is unleashed at the point of impact, inflicting 40% damage in a small radius."
03 "A cloud of shards is unleashed at the point of impact, inflicting 60% damage in a small radius."
04 "A cloud of shards is unleashed at the point of impact, inflicting 80% damage in a small radius."
05 "A cloud of shards is unleashed at the point of impact, inflicting 100% damage in a small radius."

Chemical Tipped Ordnance
01 "Chemical Tipped ordnance inflicts an additional 20% damage over time as a substance slowly eats away at them."
02 "Chemical Tipped ordnance inflicts an additional 40% damage over time as a substance slowly eats away at them."
03 "Chemical Tipped ordnance inflicts an additional 60% damage over time as a substance slowly eats away at them."
04 "Chemical Tipped ordnance inflicts an additional 80% damage over time as a substance slowly eats away at them."
05 "Chemical Tipped ordnance inflicts an additional 100% damage over time as a substance slowly eats away at them."

Cluster Cannon Ordnance
01 "Clusters of flechettes inflict a 5 degree cone of damage to target area."
02 "Clusters of flechettes inflict a 10 degree cone of damage to target area."
03 "Clusters of flechettes inflict a 15 degree cone of damage to target area."
04 "Clusters of flechettes inflict a 20 degree cone of damage to target area."
05 "Clusters of flechettes inflict a 25 degree cone of damage to target area."

Depth Charge
01 "This anti-stealth ordnance reveals stealthed aliens near the impact"
02 "This anti-stealth ordnance reveals stealthed aliens near the impact, and inflicts 20% additional damage."
03 "This anti-stealth ordnance reveals stealthed aliens near the impact, and inflicts 40% additional damage."
04 "This anti-stealth ordnance reveals stealthed aliens near the impact, and inflicts 60% additional damage."
05 "This anti-stealth ordnance reveals stealthed aliens near the impact, and inflicts 80% additional damage."

Priority Target Strongest
01 "Makes strongest alien in range the highest priority target."
02 "Makes strongest alien in range the highest priority target and inflicts an additional 20% damage."
03 "Makes strongest alien in range the highest priority target and inflicts an additional 40% damage."
04 "Makes strongest alien in range the highest priority target and inflicts an additional 60% damage."
05 "Makes strongest alien in range the highest priority target and inflicts an additional 80% damage."

Shield Buster Shells
01 "This anti-shield ordnance inflicts 20% additional bonus damage against shields."
02 "This anti-shield ordnance inflicts 40% additional bonus damage against shields."
03 "This anti-shield ordnance inflicts 60% additional bonus damage against shields."
04 "This anti-shield ordnance inflicts 80% additional bonus damage against shields."
05 "This anti-shield ordnance inflicts 100% additional bonus damage against shields."

Tachyon Shells
01 "Tachyon Shells slow down the target on impact."
02 "Tachyon Shells slow down the target on impact and inflicts an additional 15% damage."
03 "Tachyon Shells slow down the target on impact and inflicts an additional 30% damage."
04 "Tachyon Shells slow down the target on impact and inflicts an additional 45% damage."
05 "Tachyon Shells slow down the target on impact and inflicts an additional 60% damage."

Core Speed Booster
01 "Loose cores will speed up by 25% when hit by temporal pulse."
02 "Loose cores will speed up by 50% when hit by temporal pulse."
03 "Loose cores will speed up by 75% when hit by temporal pulse."
04 "Loose cores will speed up by 100% when hit by temporal pulse."
05 "Loose cores will speed up by 125% when hit by temporal pulse."

Heavier Burden
02 "Increased slowdown effect for any aliens carrying cores hit by the temporal pulse, for 25% longer."
03 "Increased slowdown effect for any aliens carrying cores hit by the temporal pulse, for 50% longer."
04 "Increased slowdown effect for any aliens carrying cores hit by the temporal pulse, for 75% longer."
05 "Increased slowdown effect for any aliens carrying cores hit by the temporal pulse, for 100% longer."

Increased Slowdown
01 "Increased Slowdown effect when a target is hit by the temporal pulse."
02 "Increased Slowdown effect when a target is hit by the temporal pulse, for 25% longer."
03 "Increased Slowdown effect when a target is hit by the temporal pulse, for 50% longer."
04 "Increased Slowdown effect when a target is hit by the temporal pulse, for 75% longer."
05 "Increased Slowdown effect when a target is hit by the temporal pulse, for 100% longer."

Depth Charge
01 "Tower deploys Stealth revealing charges."
02 "Tower deploys Stealth revealing charges, and inflicts an additional 20% damage."
03 "Tower deploys Stealth revealing charges, and inflicts an additional 40% damage"
04 "Tower deploys Stealth revealing charges, and inflicts an additional 60% damage."
05 "Tower deploys Stealth revealing charges, and inflicts an additional 80% damage."

Fire Bombs
01: "Explosive ordnance sets targets on fire for 20% additional damage over time."
02: "Explosive ordnance sets targets on fire for 40% additional damage over time."
03: "Explosive ordnance sets targets on fire for 60% additional damage over time."
04: "Explosive ordnance sets targets on fire for 80% additional damage over time."
05: "Explosive ordnance sets targets on fire for 100% additional damage over time."

Shield Buster Bombs
01 "This anti-shield ordnance is twice as effective against shields."
02 "This anti-shield ordnance is 3x as effective against shields."
03 "This anti-shield ordnance is 4x as effective against shields."
04 "This anti-shield ordnance is 5x as effective against shields."
05 "This anti-shield ordnance is 6x as effective against shields."

Cluster
01 “Shrapnel is scattered over a 20% increased radius surrounding the impact point.”
02 “Shrapnel is scattered over a 30% increased radius surrounding the impact point.”
03 “Shrapnel is scattered over a 40% increased radius surrounding the impact point.”
04 “Shrapnel is scattered over a 50% increased radius surrounding the impact point.”
05 “Shrapnel is scattered over a 60% increased radius surrounding the impact point.”

Fire Ball
01 "Fiery Impacts inflict an additional 20% damage over time on target."
02 "Fiery Impacts inflict an additional 40% damage over time on target."
03 "Fiery Impacts inflict an additional 60% damage over time on target."
04 "Fiery Impacts inflict an additional 80% damage over time on target."
05 "Fiery Impacts inflict an additional 100% damage over time on target."

Plasmaball
01 "Intense heat reduces the impact radius, but burns for an additional 30% damage over time."
02 "Intense heat reduces the impact radius, but burns for an additional 60% damage over time."
03 "Intense heat reduces the impact radius, but burns for an additional 90% damage over time."
04 "Intense heat reduces the impact radius, but burns for an additional 120% damage over time."
05 "Intense heat reduces the impact radius, but burns for an additional 150% damage over time."

Priority Target Strongest
01 "Makes strongest alien in range the highest priority target."
02 "Makes strongest alien in range the highest priority target and inflicts an additional 20% damage."
03 "Makes strongest alien in range the highest priority target and inflicts an additional 40% damage."
04 "Makes strongest alien in range the highest priority target and inflicts an additional 60% damage."
05 "Makes strongest alien in range the highest priority target and inflicts an additional 80% damage."

Bonus Versus Fastest
01 "Kinetic Rounds do 30% additional damage against the fastest aliens."
02 "Kinetic Rounds do 60% additional damage against the fastest aliens."
03 "Kinetic Rounds do 90% additional damage against the fastest aliens."
04 "Kinetic Rounds do 120% additional damage against the fastest aliens."
05 "Kinetic Rounds do 150% additional damage against the fastest aliens."

Chemical Tipped Warhead
01 "Chemical tipped warhead inflicts 20% additional damage over time to targets as substance slowly eats away with them."
02 "Chemical tipped warhead inflicts 40% additional damage over time to targets as substance slowly eats away with them."
03 "Chemical tipped warhead inflicts 60% additional damage over time to targets as substance slowly eats away with them."
04 "Chemical tipped warhead inflicts 80% additional damage over time to targets as substance slowly eats away with them."
05 "Chemical tipped warhead inflicts 100% additional damage over time to targets as substance slowly eats away with them."

Priority Target Strongest
01 "Makes strongest alien in range the highest priority target."
02 "Makes strongest alien in range the highest priority target and inflicts an additional 20% damage."
03 "Makes strongest alien in range the highest priority target and inflicts an additional 40% damage."
04 "Makes strongest alien in range the highest priority target and inflicts an additional 60% damage."
05 "Makes strongest alien in range the highest priority target and inflicts an additional 80% damage."

Shrapnel Warhead
01 "A cloud of shrapnel is unleashed around the point of impact, inflicting damage in double the normal radius."
02 "A cloud of shrapnel is unleashed around the point of impact, inflicting damage in 3 times the normal radius."
03 "A cloud of shrapnel is unleashed around the point of impact, inflicting damage in 4 times the normal radius."
04 "A cloud of shrapnel is unleashed around the point of impact, inflicting damage in 5 times the normal radius."
05 "A cloud of shrapnel is unleashed around the point of impact, inflicting damage in 6 times the normal radius."

Temporal Missile
01 "Tachyon Warheads slow down the target significantly on impact."
02 "Tachyon Warheads slow down the target significantly on impact, and inflict an additional 15% damage."
03 "Tachyon Warheads slow down the target significantly on impact, and inflict an additional 30% damage."
04 "Tachyon Warheads slow down the target significantly on impact, and inflict an additional 45% damage."
05 "Tachyon Warheads slow down the target significantly on impact, and inflict an additional 60% damage."

Depth Charger
01 "This anti-stealth charge reveals any stealthed alien hit."
02 "This anti-stealth charge reveals any stealthed alien hit, and inflicts an additional 20% damage."
03 "This anti-stealth charge reveals any stealthed alien hit, and inflicts an additional 40% damage."
04 "This anti-stealth charge reveals any stealthed alien hit, and inflicts an additional 60% damage."
05 "This anti-stealth charge reveals any stealthed alien hit, and inflicts an additional 80% damage."

Priority Target Strongest
01 "Makes strongest alien in range the highest priority target."
02 "Makes strongest alien in range the highest priority target and inflicts an additional 20% damage."
03 "Makes strongest alien in range the highest priority target and inflicts an additional 40% damage."
04 "Makes strongest alien in range the highest priority target and inflicts an additional 60% damage."
05 "Makes strongest alien in range the highest priority target and inflicts an additional 80% damage."

Shield Cracker
01 "This anti-shield energy bolt inflicts 20% bonus damage to the target's shields."
02 “This anti-shield energy bolt inflicts 40% bonus damage to the target’s shields.”
03 “This anti-shield energy bolt inflicts 60% bonus damage to the target’s shields.”
04 “This anti-shield energy bolt inflicts 80% bonus damage to the target’s shields.”
05 “This anti-shield energy bolt inflicts 100% bonus damage to the target’s shields.”

Shocker
02 "Targets remain "charged" after hit by energy bolt, which will shock other passing aliens for 20% additional damage."
03 "Targets take an additional 40% damage and remain "charged", shocking any aliens they come in contact with for 20% damage."
04 "Targets take an additional 60% damage and remain "charged", shocking any aliens they come in contact with for 20% damage."
05 "Targets take an additional 80% damage and remain "charged", shocking any aliens they come in contact with for 20% damage."

Special thanks to these players for contributing information used in this guide:

Platinawolf
Miraglyth
Alkydere
Cmdr Skittles
Marbur
xumm2012
CH_Wolfe
AxeMurderer
ifthisisthenthat
X-heketchis_V44
Nemo
avanidk
Protoss
PaulC2K
[TEA] Breet
devid3an
John Wilkes Bluetooth
Howl
Hodge Mann