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