Okay, I will answer... Don't want to be too cruel

You have to finish certain quests to get different hats:
1)
brown hair (which looks like

)
Finish "Mad Hatter" (5

5

10

)
2)
Tuber's cloakBeat Tuber and take his cloak
3)
Mario's hatFinish the quest "Mushrooms Hunter" (1

1

1

1 golden mushroom). You can finish this quest after you got the book of mushrooms.
4)
Undefined woollen hatFinish "Eco-Terrorist pony" (10

10

3 moneybags)
The first two are not too hard to get because the items are not really rare (Tuber's cloak is coeff 0, you "only" have to beat Tuber, which you will be able to do some time in the future; and the hats are coeffs 3 and 4, which does not take eternally to get), but the other two are really hard - the moneybag is coeff 5, and getting 3 of them can take a while (I still want to see my 3rd one... and I have played for, I think, more than a year now. Or even longer?) and the golden mushroom is even coeff 6!