Super Onion Boy 2 (US)

You need to collect 40 stars in total.
You can get 5 stars in a level so we're going to play 8 levels
In my video I go through the levels and show where the stars are

level 1: 1:05
Level 2: 2:35
Level 3: 4:10
Level 4: 5:45
Level 5: 6:45
Level 6: 8:20
Boss: 9:55
Level 7: 10:20
Level 8: 11:55

Achievement Walkthrough:

Here's my Achievement Walkthrough with commentary running you through the first 8 levels and collecting 40 stars.
Timecodes:
Intro 0:00
Level 1 1:07
Level 2 2:51
Level 3 4:27
Level 4 6:03
Invincibility 6:35
Level 5 7:05
Level 6 8:50
Blue Jellyfish Boss 10:25
Level 7 11:04
Level 8 12:25
Forty Stars 13:30