Here is the full list of all 75 GIBZ achievements.
Unlock all hats and facewear
Use the Dynamite Launcher to launch yourself backwards rapidly (unlocks Combat Helmet)
[Base Defence] Have 4 fully decked out Survivors in your base
[Base Defence] Clear 200 Waves
[Base Defence] Have a Boss reach 0 health without a single player damaging them
[Base Defence] Unlock everything under the Survivor Tree
[Halloween] Go Trick-or-Treating wearing a Halloween themed item
[Xmas] Get a Snowman Head
[Halloween] Eat 200 pieces of candy (unlocks the Witch Hat and Nose)
[Base Defence] Unlock everything under the Building Tree
[Halloween] Find and unlock the Spitter and Werewolf Masks
[Halloween] Smash 100 Pumpkins (unlocks the Pumpkin Head)
[Xmas] Find and collect the Antlers off the "Deerwolf" (unlocks Antlers)
Unlock every weapon
Beat the final boss having never lowered the difficulty below HARD on that character (unlocks Broadsword)
Beat the final boss having never lowered the difficulty below HARD or spent any money on that character (unlocks Dark Knight Helmet)
Hit a stick of dynamite 7 times back and forth with a friend
[Base Defence] Don't let a single chicken damage anything during a wave of chickens
[Base Defence] Clear 100 Waves
Chop down some stumps (unlocks Wood Axe)
Max out all stat buffs
[Base Defence] Clear 20 Waves
[Base Defence] Ring the bell several times in a row
Cut up a bunch of fish (10) in a row without being hit by one (unlocks Headband and Blindfold)
Hit back 262 projectiles (unlocks Baseball Bat)
Win a game of Defence without taking any damage
Revive 5 bosses (unlocks the Army Hat)
Defeat your friends (unlocks Hood)
Defeated the Wizard
Beat the final boss having never lowered the difficulty below EASY on that character
Beat the final boss having never lowered the difficulty below NORMAL on that character
Have 30+ maggots on you at once
Kill 600 enemies with fire (unlocks the Black Gas Mask)
Give the Machete Slinger a taste of his own medicine (unlocks the Bloody Metal Mask)
Use the Lever-action rifle to teach some big monsters a lesson (unlocks the Black Cowboy Hat)
Kill a Crusher by only hurting it with it's own rocks until it gets angry, then proceed to not take any damage from it (unlocks the Dark Crusher Mask)
Killed the Skeleton Goliath
Dodge roll 2,500 times (unlocks Dark Aviator Goggles)
Heal 5 hearts using the heal dance on normal difficulty or higher (unlocks the Custom Cap)
Clear the Tower Bridge
Clear the Tower Bridge, having all the bosses chasing you at once
Cut off 1,000 limbs with the Bone Chainsaw
Killed the Surgeon boss
Kill 1,000 enemies with explosives (unlocks Mining Helmet)
Kill 2,500 enemies with auto-rifles
Kill 1,000 enemies with Supa MGs
Earn a total of £50,000
Kill 2,500 enemies with melee weapons
Kill a total of 25,000+ enemies
Dig 750 holes
Decapitate 10,000 zombies
Kill 2,500 enemies with shotguns
Kill 1,000 enemies with Supa Shotguns
Shoot off 5,000 pairs of zombie legs
[Xmas] Get a Festive hat off a Zombie or a Friend (unlocks Santa Hat)
Repel a lot of zombies (unlocks the Plague Doctor Mask)
Amputate 8,000 zombie arms
Play Zombie Surfing 10 times
Open 300 crates
Found and unlocked the Taller Top Hat
Unlock all perks
Play 10 mini-games (unlocks the Pith Helmet)
Kill 1,000 enemies with Supa Snipers
Kill 500+ zombies in a single round of Mayhem (singleplayer)
Die a lot (unlocks the Tall Top Hat)
Kill 2,500 enemies with single-shot rifles
Find a great photo opportunity
Killed the Goliath boss
Headshot 400 zombies with single-shot rifles (unlocks the Dark Steampunk Goggles)
Kill 600 enemies with sidearms
Headshot 300 zombies with sidearms (unlocks the Custom Bandit Mask)
Killed the Fisherman boss
Killed the Glutton boss
Kill 10 zombies with one shockwave in Zombie Surfing
Killed the Machete Slinger boss