The Chosen Ones

To summon the living tree you have to click on 10 wisps (after receiving the quest from 3 heroes on the road) - wisps are appearing randomly in time but in the same (so to say) screen as your hero is standing or moving. You got about 2 seconds to click the wisp - and you have to do it 10 times - don't worry - the wisps would keep appearing (you don't need to click 10 in a row). After finishing this you will face the Boss in the lair - (located to the left from the cave entrance). The Boss has different phases - one of which is when he moves to the form of a big wisp and it is hard to see him as far as the screen became greener and greener. To finish such phase you just have to attack the wisps several times - he moves faster than you in random directions - just wait until he moves near of your hero and attack.
Good Luck!