Here is the full list of all 19 Stewart The Fox achievements.
Finish the fourth level to get this achievement
Kill the second boss in level 4
Find all collectable Gifts.
Finish the third level to get this achievement
Kill the first Boss in level 3
Kill 25 Enemies.
Finish the second level to get this achievement
Finish the first level to get this achievement
Finish level 1 in under 3.5 minutes!
Finish level 2 in under 3.5 minutes!
Finish level 3 in under 3.5 minutes!
Finish level 4 in under 3.5 minutes!
Kill 50 Enemies.
Kill 75 Enemies.
Kill 100 Enemies.
Find all collectable TV's.
Find all collectable Orb's.
Find all collectables throughout the game!
Finish a level without dying.