Here is the full list of all 75 GIBZ achievements.
Unlock all hats and facewear
Hit a stick of dynamite 7 times back and forth with a friend
[Base Defence] Clear 200 Waves
Use the Dynamite Launcher to launch yourself backwards rapidly (unlocks Combat Helmet)
[Base Defence] Ring the bell several times in a row
[Base Defence] Clear 100 Waves
[Base Defence] Have a Boss reach 0 health without a single player damaging them
[Base Defence] Don't let a single chicken damage anything during a wave of chickens
[Base Defence] Have 4 fully decked out Survivors in your base
[Base Defence] Clear 20 Waves
[Base Defence] Unlock everything under the Building Tree
[Base Defence] Unlock everything under the Survivor Tree
Headshot 300 zombies with sidearms (unlocks the Custom Bandit Mask)
Defeat your friends (unlocks Hood)
[Xmas] Get a Snowman Head
[Xmas] Find and collect the Antlers off the "Deerwolf" (unlocks Antlers)
[Halloween] Eat 200 pieces of candy (unlocks the Witch Hat and Nose)
[Halloween] Smash 100 Pumpkins (unlocks the Pumpkin Head)
[Halloween] Find and unlock the Spitter and Werewolf Masks
[Halloween] Go Trick-or-Treating wearing a Halloween themed item
Dodge roll 2,500 times (unlocks Dark Aviator Goggles)
Revive 5 bosses (unlocks the Army Hat)
Cut off 1,000 limbs with the Bone Chainsaw
Kill a total of 25,000+ enemies
Unlock every weapon
Chop down some stumps (unlocks Wood Axe)
Kill 600 enemies with fire (unlocks the Black Gas Mask)
Kill 600 enemies with sidearms
Kill 1,000 enemies with Supa Snipers
Hit back 262 projectiles (unlocks Baseball Bat)
Decapitate 10,000 zombies
Kill 1,000 enemies with explosives (unlocks Mining Helmet)
Die a lot (unlocks the Tall Top Hat)
Cut up a bunch of fish (10) in a row without being hit by one (unlocks Headband and Blindfold)
Shoot off 5,000 pairs of zombie legs
Give the Machete Slinger a taste of his own medicine (unlocks the Bloody Metal Mask)
Max out all stat buffs
Play Zombie Surfing 10 times
Win a game of Defence without taking any damage
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
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)
Clear the Tower Bridge, having all the bosses chasing you at once
Earn a total of £50,000
Have 30+ maggots on you at once
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)
Kill 2,500 enemies with single-shot rifles
Use the Lever-action rifle to teach some big monsters a lesson (unlocks the Black Cowboy Hat)
Heal 5 hearts using the heal dance on normal difficulty or higher (unlocks the Custom Cap)
[Xmas] Get a Festive hat off a Zombie or a Friend (unlocks Santa Hat)
Find a great photo opportunity
Amputate 8,000 zombie arms
Open 300 crates
Play 10 mini-games (unlocks the Pith Helmet)
Kill 2,500 enemies with shotguns
Kill 500+ zombies in a single round of Mayhem (singleplayer)
Kill 1,000 enemies with Supa Shotguns
Kill 2,500 enemies with auto-rifles
Kill 1,000 enemies with Supa MGs
Repel a lot of zombies (unlocks the Plague Doctor Mask)
Kill 2,500 enemies with melee weapons
Unlock all perks
Dig 750 holes
Killed the Skeleton Goliath
Clear the Tower Bridge
Headshot 400 zombies with single-shot rifles (unlocks the Dark Steampunk Goggles)
Killed the Surgeon boss
Killed the Goliath boss
Kill 10 zombies with one shockwave in Zombie Surfing
Found and unlocked the Taller Top Hat
Killed the Fisherman boss
Killed the Glutton boss
Killed the Machete Slinger boss