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