by EML, age 7
I went to every place in goat mmo simulator and no demon.
I looked in Old Goat Mountain. I found the old goat and no demon. In Android version, there was a blue portal near a tent. I went in and I was in a stone room. It wasn't fair to send me on a quest to get a demon horn. I couldn't find the demon. The portal to riches isn't true.
If we find out more at a later date, we will update this post. If you can help answer this question, please leave a comment below.
update: by EML age 8
I did find the answer. I was looking in the wrong place, or I missed it the first time. On Garblage Beach, there is a blacksmith place, near the gold hammer statue. On the right of it is the demon horn - no one has it, it is just laying there. When you find it, go back to Dumbledore and give it to him. And the portal of riches quest is done.