Earn 3 stars in every level in area 1. (Levels 1-12)
Feed and level-up Pigger to level 9.
Feed and level-up Naqua to level 9.
Earn 3 stars in every level in area 2. (Levels 13-25)
Earn 3 stars in every level in area 3. (Levels 26-40)
Feed and level-up Feline to level 9.
Feed and level-up Bumble Bee to level 9.
Earn 3 stars in every level in area 4. (Levels 41-65)
Earn 3 stars in every level in area 5. (Levels 66-100)
Feed and level-up Ponypop to level 9.
Earn 3 stars in every level in area 6. (Levels 101-130)
Feed and level-up Coral to level 9.
Feed and level-up Ruff to level 9. (Unlock him via the friend-invites menu accessible from the map)
Earn 3 stars in every level in area 7. (Levels 131-160)