Find the source of the choking roots Overlord Guide

Turn right to meet two anemic half-dead elves (#1) and find out there are two crazy bloody unicorns to kill. The first one you'll meet just after the elves (#2) - to the left. Kill it! (you can slow it down with your spell, throw some fireballs and attack with your minions withdrawing your commando from time to time to avoid casualty). Keep going and you'll come to a stream. Don't send your minions there cause they'll surely drown! Just cross it yourself first and the'll find a branch or something (on the left) to catch up safely. There's the second bloody unicorn waiting for you - kill it the same way or try some other tactics yourself.

Now, there's a barrier on your right (#1) and a spell behind it. Send your minions to the wheel near by (#2) to make the bridge. Take the spell to teleport and come back to the place where you met the elven ghosts (follow the path and turn right). Break the barrier past them and continue killing the forest creatures you'll meet on the way. Watch the scene so you'll get an idea as of what is actually going on around the area.