Island of Druid

A great island where Tieru once lived; his spirit still resides there. But the demons didn't want to share their world with the elves. Having captured everything around the island, they wanted to seize it as well. Tieru didn't like the pitiful attempts of the demons to capture his island. After destroying three demon cities, he drove them north, beyond the mountains. Since then, the demons have not bothered the elves. But it seems they need the island of Tieru again. And although Tieru himself is no longer alive, the island is still as strong and impregnable. At all costs, Ossir must protect the island from the demons and destroy the remaining two demon cities!
This is my first map ever, so please don't judge too harshly. I ask all map makers: please advise what needs to be added and what needs to be fixed; thank you in advance