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