Here is the full list of all 16 Iris and the Giant achievements.
Achieve Skeleton challenge
Achieve Sleeping Cyclop challenge
Achieve bat challenge
Achieve Wide Mouth challenge
Achieve Baby Snake challenge
Achieve Cat Thief challenge
Achieve Baby Boar challenge
Achieve Tiny Cyclop challenge
Achieve Fire Bat challenge
Achieve Mimic challenge
Achieve Tiny Fire challenge
Achieve Baby Minotaur challenge
Achieve Hunter challenge
Achieve Sad Skeletong challenge
Achieve Cerberus challenge
Achieve Tiny Lightning challenge