Credits to Monoxide Child at the xbox360 achievements forums and Chamaelleo.
Animal Name :: Animal Power :: Area :: Description
1. Chicken :: Increase to defense, strength and agility :: Flooded Temple :: First dry land section, there's an X right in front of two giant fish statues in the background. Dig there.
2. Cardinal :: Helps you find secret items :: Industrial Castle :: Top floor of castle, kill the brute and get the Cardinal.
3. Owlet :: Retrieves hidden fruit from trees :: Forest Entrance :: Right before you exit the deadlands go behind the overgrown area and swing your weapon.
4. Mr Buddy :: Helps you dig faster :: Home Castle :: Go back into the first room where all the tutorial people are. At the back far wall, near the veterinary lady, there's an X on a pile of straw. Dig it up.
5. Giraffey :: Helps you level up faster :: Desert :: Look for the X shapes on the sand (or have Pazzo as your animal :: he'll show you where to dig), the giraffe is one of the last ones before the end of the level.
6. Snoot :: Increases your strength :: Cyclops' Fortress :: Bomb the cracked wall in the very first room. It's located to the left of the first light you see on the floor and to the right of the painting and column that casts a shadow.
7. Piggy :: Makes food give you more health :: Swamp Village Store :: Purchased for 585 gold.
8. Zebra :: Helps you find food in grass :: Desert Chase :: Taken from the guy on the camel, when you see him run off, follow as fast as you can (on the back of another camel, obviously). You'll need to dodge the quicksand, and then use an arrow to knock him off his camel before he reaches safety.
9. Rammy :: Knocks down enemies :: Tall Grass Field :: Taken from the large bear with the banner.
10. Spinny :: Increases your defense :: Volcano Store :: Purchased for 680 gold.
11. Bitey Bat :: Chomps enemy's heads :: Pipistrello's Cave :: Found after the boss bat.
12. Troll :: Slowly regenerates your health :: Thieves Forest :: Behind a wall, use 3 bombs to set him free.
13. Frogglet :: Can pick up items with his tongue :: Marsh :: Halfway through the first graveyard, the X is directly in front of an open crypt, just before the wall goes back and the area widens.
14. Seahorse :: Allows you to move quickly through water :: Thieves Forest :: Right after the dear leaves a poo streak and before the stream in the forest.
15. Snailburt :: Increases your defense but decreases your agility :: Marsh :: Towards the end, he is right out in the open so you cant miss him.
16. Scratchpaw :: Increases your strength and agility :: Sandcastle Interior :: There are two barred windows at the back of the room, the tiger is behind the second one. Use bombs on the cracked wall to get to him.
17. Yeti :: Protects you from being frozen :: Snow World :: As you go down the ramp and check behind the huts.
18. Monkeyface :: Increases your luck finding items :: Church Store :: Purchased for 750 gold.
19. Pazzo :: Helps you find buried treasures :: Snow Store :: Purchased for 750 gold.
20. Sherbert :: Helps you jump higher :: Animal Art :: Hiding near the ceiling at the back of the animal ark. Stand underneath him, hold RT and press A. You'll do a magic-boosted jump and reach him straight away.
21. Meowburt :: Increases your agility :: Parade :: This can be found by backtracking from cyclops fortress to the area at the end of parade, when you get hit by the tunnel you'll land on the ground and if you see a bush in the middle go behind the bush and Meowburt should appear.
22. Hawkster :: Attacks fallen enemies :: Tall Grass Field :: Blow the horn outside the huts just before you get Rammy.
23. Burly Bear :: Increases your strength :: Tall Grass Field :: With a sandwich and a couple of bombs. Go to where you climb up the grass section of the cliff but don't go up, instead head to the left side of the cliff, eat the sandwich and you'll find you can move the rock on the side. Inside there are two chests and a crack in the wall, the bear is in the crack.
24. BiPolar :: Mauls Enemies (and Friends) who are near death :: Snow World :: As you walk up the ramp, use the horn by the sign post signaling it. He pops out of the tunnel.
25. Beholder :: Gives you a magical boost :: Full Moon :: Play through the level with Cardinal as your animal. At the second hut up the mountain path, it'll bring you a golden key "weapon". This unlocks the padlocked door in the ark, and inside is the Beholder.
26. Install Ball :: Shoots enemies with his photons :: Alien Ship :: Play through until the countdown begins. Shoot the mechanism that destroys the first green laser gate (after the toilet) and head straight up. There's a door there (hard to see what with it being dark etc). Go left slightly. It's still possible to exit the ship before the countdown ends - not that it actually matters.