This list is outdated. A lot of avatars have been released that I never added to this list. One day I might get back to it. It sure would be nice if I could remember what (F) and (A) mean.

WORKING ON:
None at the moment.

BATTLE:
Bailiff - Beat Bailiff 15 times in one-player battle arena.
Balloon - Have Balloon Trading Card in your Deck and view it.
Cake - Have Cake Trading Card in your deck and view your Deck.
City Accountant - Battle City Accountant 17 times.
City Banker - Battle City Banker 19 times.
City Hobo - Battle City Hobo once and view Battle Opponents page.
City Realtor - Battle City Realtor 22 times.
Daemon - Beat Daemon 23 times in the Battle Arena.
Elder - Win battle against Elder 400 times in the battle arena.
Evil Tree - Beat Evil Tree 35 times in the battle arena.
Flamed - Beat Flamed 276 times in the one-player battle arena.
Gobble Voodoo Doll - Have a Gobble Voodoo Doll Trading Card in your Deck then view Deck.
Hades - Beat Hades 29 times in the one-player battle arena.
Hero - Beat Hero 110 times in the one-player battle arena.
Hot Dog - Beat Hot Dog 375 times in the one-player battle arena.
Impossible - Beat Devil once in the one-player battle arena.
Lightning Gobble - Have a Lightning Gobble Trading Card in your Deck then view Deck.
Muguel - Buy a Muguel Trading Card from the Kwazikujo Shop.
Mutant Gobble - Have a Mutant Gobble Trading Card in your Deck then view Deck.
Phospho - Lose to Phospho in the one-player battle arena.
Rusty - Beat Rusty 226 times in the one-player battle arena.
Snowball - Beat Snowball 60 times in the one-player battle arena.
Stellar - Random when beating Stellar in a one-player battle arena.
Sultan - Beat Sultan once in the one-player battle arena.
Twree - Have a Twree in your Deck and another in your Inventory then view your deck.
Vibue - Draw against Vibue in the one-player battle arena.
Warrior - Win 50,000+ battles then view the Stats tab on your profile.

COSTUMES:
Advent - Use an Advent Tree Costume on your pet.
Armoured - Use an Armoured Costume on your pet.
Dark Fairy - Use a Dark Fairy costume on your pet.
Dragon - Use a Dragon costume on your pet.
Enpiah - Use an Enpiah costume on a Gonk pet

BASPINARS CASTLE
Use any Enchanted Oglue Plushie or Oglue Potion

BIALA MOUNTAIN
Own any pet wearing an Advent Costume

CANDYLAND
Complete 500 or more Candy Tree quests

CITY SEWERS
Complete 400 or more Sewer Monster quests

CITY OF MARADA
Complete 500 or more Garage quests

DUKKA CAVES
Own any pet wearing a Wizard Costume

ELEKAS CASTLE
Win any item Bonus Prize from Apprentice Wizard

ENPIAH
Complete 200 or more Cosmonaut quests

FOXFIRE FOREST
Visit the Foxfire Pond and gain a Stat for your pet

GIGANTIC PARADISE
-done-

JENOA
Use any Enchanted Kronk Plushie or Kronk Potion

KAMILAH DESERT
Win 25,000MP or more from Jackpot Pyramid

LOWLYHOOD
Complete 1 Episode or more of Happy Hour

LUSH LAKE
-done-

MINIPET ISLAND
-done-

NIMBUS
-done-

PUCHALLA VILLAGE
Complete 500 or more Puchalla Inn quests

SIMERIA
-done-

SLATER PARK
-done-

UNDYING WOODS
-done-

VORTEX PARK
Complete 300 or more Travis Truck quests

ZIRANEK
Complete 350 or more Computer Repair Quests

Mission related levels
Quest related levels
Pet colour/Costume related levels
Done

This is an incomplete list of cheaper items in order of rarity.
Many, many thanks to OrangeFrappucino`s marasite. For the complete list please visit:
http://www.marasites.com/?name=OrangeFrappucino&page=RarityListforPoisonPit

Rarity 1
Blue Gumball
Yellow Gumball
Fish Tails
Rowan
Hawthorn

Rarity 2
Milk Chocolate Gumball
Orange Chocolate Gumball
Fiddlehead
Celery

Rarity 3
Tanning Salon Ticket
Fish Eyes
Rock Gumball

Rarity 4
Tombola (DVD)
Starry Gumball

Rarity 5
Gigantic Fairy Mallet
Tombola Book
Tombola Stamp
Bronze Gumball

Rarity 6
Fake One Dukka Coin
Fake Two Dukka Coin
Fake Three Dukka Coin
Fake Four Dukka Coin

Rarity 7
Eleka Tombola Book
Eleka Tombola (CD)
Orange Gumball

Rarity 8
Fake Six Dukka Coin
Fake Eight Dukka Coin
Wormy Apple
Eleka Tombola Stamp

Rarity 9
Eleka Tombola Balloon
Puppy Love Candy Heart
Blue Fasoro Balloon
Green Gumball

Rarity 10
Test Your Strength Potato
Lush Lake Ticket
Tombola Tunes
Invisible Gumball

Rarity 11
Trash Potato
Free Male Plastic Surgery Coupon
Free Female Plastic Surgery Coupon
You Better Run Candy Spade

Rarity 12
Satyr Potato
Test Your Strength Pearl
Ewww Candy Spade

Rarity 13
Satyr Action Figure
Undying Tombola (DVD)
Ant Hill Cake

Rarity 14
Yuni Brows Coupon
Green Phanty Balloon
Four Cheese Pizza

Rarity 15
Undying Stamp
Jerk Candy Spade