Sitting up on that tree branch might be serving you well at the moment but keep a good eye on that Runespoor, it's already using all the muscles in it's body to help it work it's way up the tree.

Three forked tongues flick out of the three mouths and angry hissing can be heard clearly. Making the Runespoor climb it's way to you sure is causing it to become upset.

Choosing just the right head to aim your spells at was a good start. Stupefy hit the right head straight on but all it really did was anger the creature, it's fangs baring at you now and the hissing growing louder. That Confundo charm did the trick however, the right head blinked it's eyes and the hissing stopped. Confusing that head seemed to have worked but don't forget about the other two heads.

Best continue to make good use of that Aquamenti spell, the dampness of the water on your head and clothes will only last so long.

The left and middle heads are still forcing the right head to go along with them, the Runespoor still aiming to make it's way up the tree to where you are, though slower now.

Don't forget you have another line of Runes on the door you need to decipher in order to get out of here.