Stoick's Challenges: baaaack to berk

I don't know where all of the 20 sheep are, but I know some of them:
1. In the cave that is between the 2 mountains. Fly a little bit into it and you'll find it in there.
2. I think there is one on the little islan next to the arena.

I know how you feel! I've just completed this challenge myself it is no doubt the hardest challenge.
There is five sheep on the sea stacks (mini islands) in the cave entrance a top of mountain there's one in the entrance and two in the lowest chamber at the exit there's a sheep not far from the hole you came out of if you keep flying around close to the ground there is another sheep,by the crown of the alpha sweep the sheep there is a sheep by the blue and red post. There are sheep by all the sweep the sheep challenges. At the lowest cave entrance by the sea turn around and fly up the big arch there you will find another sheep. Thgo to the meridian of misery tournament perch fly straight up you'll find two peaks on the highest one is where the sheep is. Fly up from the village until you reach the highest point on the mountain fly downward till you pass some clouds there you will find another sheep hope this helps!