Terraria

There are certain items in the game that summon pets when used. This achievement is earned by finding and using all the pet summoning items in the game. They are found randomly in chests, and some are dropped by certain mobs. The quickest way to get this achievement is to head over to the Item/Weapon/Armor Trading thread and make friends.

Listed below are they ways to get each pet summoning item:
*Please note that "chests" refers to normal wood chests

If you want to find them all in single player, the best advice I can give is to open every chest you find. The locations I've listed below were compiled from a month's worth of various Terraria message board posts. They may not be completely accurate, and you may find a pet at a different location.

• Cabbage Summons a Guinea Pig. Found in chests and gold chests. Has an unknown chance of being dropped by Dragon Snatchers in the Jungle.
• Petri Dish Summons a Slime. Found in chests and gold chests. More common in the Dungeon.
• Vial of Blood Summons a Bat. Found in gold chests. More common in the Dungeon with a 10% chance of dropping from a Vampire Miner.
• Brain Summons a Zombie. Found in gold chests and shadow chests. Has an unknown chance of being dropped by The Groom. Can sometimes be found in gold chests located near the top of the Underworld layer.
• Wolf Fang Summons a Werewolf. Found in gold chests in the wooden structures located in the cavern layer. Has an unknown chance of being dropped by a Werewolf.
• Honeycomb Summons a Tiphia (Hornet). Found in gold chests in the lower part of the Underground Jungle and ivy chests. Has an unknown chance of being dropped by a Dragon Hornet.
• Amber Mosquito: Summons a Baby Dinosaur. Has a 1 in 5000 chance of dropping as a result of putting silt or slush into an Extractinator.
• Fish: Summons a Baby Penguin. Found in ice chests in the Underground Snow.
• Bone Key: Summons a Baby Skeletron Head. Always dropped after killing the Dungeon Guardian. Can only be obtained in a world where Skeletron has not been defeated.
• Parrot Cracker: Summons a Parrot. Sold by the Pirate NPC if he is living in an ocean biome.
• Seaweed: Summons a Turtle. Found in Ivy chests.
• Strange Glowing Mushroom: Summons a Baby Truffle. Purchased from the Truffle NPC.
• Toy Sled: Summons a Baby Snowman. 5% chance of dropping from a Mimic in an ice biome.
• Eater's Bone: Summons a Baby Eater. Has a 3.33% chance of dropping from the final segment of the Eater of Worlds.
• Nectar: Summons a Baby Hornet. Has a 5% chance of being dropped byy the Queen Bee.
• Lizard Egg: Summons a Lizard. Has a 0.03% chance of dropping from Lihzahrds and Flying Snakes in the Lihzahrd Temple.
• Seedling: Summons a Sapling. Has a 5% chance of being dropped by Plantera.
• Tiki Totem: Summons a Tiki Spirit. Sold by the Witch Doctor NPC when living in Jungle biome.
• Eye Spring: Summons an Eyeball Spring. Has a 2% chance of dropping from an Eyezor.
• Cursed Sapling: Summons a Cursed Sapling. Has a chance to be dropped by Mourning Wood during the Pumpkin Moon event.
• Spider Egg: Summons a pet spider. Has a chance of being dropped by Pumpking during the Pumpkin Moon event.

Note: The Carrot is a PC-exclusive item only available to those who purchased the Collector's Edition of Terraria. It doesn't exist on consoles.

There are certain items in the game that summon pets when used. This achievement is earned by finding and using all the pet summoning items in the game. They are found randomly in chests, and some are dropped by certain mobs. The quickest way to get this achievement is to head over to THIS THREAD and make friends.

Listed below are they ways to get each pet summoning item. Please note that "chests" refers to normal wood chests. If you want to find them all in single player, the best advice I can give is to open every chest you find. The locations I've listed below were compiled from a month's worth of various Terraria message board posts. They may not be completely accurate, and you may find a pet at a different location.
 

• Cabbage - Summons a Guinea Pig. Found in chests and gold chests. Has an unknown chance of being dropped by Dragon Snatchers in the Jungle.
• Petri Dish - Summons a Slime. Found in chests and gold chests. More common in the Dungeon.
• Vial of Blood - Summons a Bat. Found in gold chests. More common in the Dungeon with a 10% chance of dropping from a Vampire Miner.
• Brain - Summons a Zombie. Found in gold chests and shadow chests. Has an unknown chance of being dropped by The Groom. Can sometimes be found in gold chests located near the top of the Underworld layer.
• Wolf Fang - Summons a Werewolf. Found in gold chests in the wooden structures located in the cavern layer. Has an unknown chance of being dropped by a Werewolf.
• Honeycomb - Summons a Tiphia (Hornet). Found in gold chests in the lower part of the Underground Jungle and ivy chests. Has an unknown chance of being dropped by a Dragon Hornet.
• Amber Mosquito - Summons a Baby Dinosaur. Has a 1 in 5000 chance of dropping as a result of putting silt or slush into an Extractinator.
• Fish - Summons a Baby Penguin. Found in ice chests in the Underground Snow.
• Bone Key - Summons a Baby Skeletron Head. Always dropped after killing the Dungeon Guardian. Can only be obtained in a world where Skeletron has not been defeated.
• Parrot Cracker - Summons a Parrot. Sold by the Pirate NPC if he is living in an ocean biome.
• Seaweed - Summons a Turtle. Found in Ivy chests.
• Strange Glowing Mushroom - Summons a Baby Truffle. Purchased from the Truffle NPC.
• Toy Sled - Summons a Baby Snowman. 5% chance of dropping from a Mimic in an ice biome.
• Eater's Bone - Summons a Baby Eater. Has a 3.33% chance of dropping from the final segment of the Eater of Worlds.
• Nectar - Summons a Baby Hornet. Has a 5% chance of being dropped byy the Queen Bee.
• Lizard Egg - Summons a Lizard. Has a 0.03% chance of dropping from Lihzahrds and Flying Snakes in the Lihzahrd Temple.
• Seedling - Summons a Sapling. Has a 5% chance of being dropped by Plantera.
• Tiki Totem - Summons a Tiki Spirit. Sold by the Witch Doctor NPC when living in Jungle biome.
• Eye Spring - Summons an Eyeball Spring. Has a 2% chance of dropping from an Eyezor.
• Cursed Sapling - Summons a Cursed Sapling. Has a chance to be dropped by Mourning Wood during the Pumpkin Moon event.
• Spider Egg - Summons a pet spider. Has a chance of being dropped by Pumpking during the Pumpkin Moon event.

Note: The Carrot is a PC-exclusive item only available to those who purchased the Collector's Edition of Terraria. It doesn't exist on consoles.