The rules that bing able to earn Greens for YooHoo Stickers is changed from AUG 3.
Please see the below rules about earning Greens.
What are Green and how do I get them?
Green is the unit of online point that players earn using various content in the YooHoo website.
These Green are then traded in for YooHoo Stickers.
There are many ways to save Green on Yoohoofriends.com!
1) When you register as a member of YooHoo website, 100 Greens are saved.
2) Each day that you log into the website, 1 Greens are saved.
3) When you watch one animation video, 2 Greens are saved.
4) When you download content off the YooHoo & Friends website, 1 Greens are saved.
5) When you earn 500 points while playing games, 1 Green is saved.
6) When you click "I like this character" on the character bios, 2 Greens are saved.
7) When you write one comment, 2 Greens are saved.
Plus, You can check the second question in Help page again.
Go see 'Help' page