And there you have it - a brand new goal in life: kill Oberon. It will take you quite some time and adventure before you finally make it but what else are you here for?! Now break the barrier to your right (#1) and walk further. Use the blood pit there if you need. Look at this strange root with a pulsating sphere of light at its ending! Send your minions to destroy it (#2). You better start enjoying this cause there are 5 more of these nodes to cut.
Now come back and turn into the path blocked by the root before. There are some poisonous plants. Keep walking, fight the forest creatures and you'll meet some magical beasts performing a ritual - Gnarl will show you a poisonous plant which will help you defeat them. Just send one minion to carry it to the creatures so they get poisoned and die. Now go across the water (#1) to the other side - your minions will find a way to follow you there. You'll find another poisonous plant (#2) - use it the same way to fight the next opponents.
Walk across the water, kill more forest creatures and collect some stuff on your way. Now stop -there are two groups of enemies: on your left and in front of you (#1). Guide one minion with the poisonous plant to the island on the left - they should all die, but fight them if they don't. Send the next one to the gathering ahead (the plant is by the tree, to the left). Walk further, break the barrier and you'll see next of these plants - carry it to the beasts dancing near by (#2). If some of them survive, bring them another one.
Break another barrier (#1) and you'll see - green minions! They'll show you a shortcut to the cave - but before you follow them - collect the tower object you'll find on your left. Send your fellows to the mechanism to the left to make a pass and they will know their way to the nearest waypoint. Now your mana has increased! Go to the cave then - it's to the left from the place where you've found the object.