Moonwort
Moonworts skin turns to bark and leaves cover him as he grows to fill the room. He rushes at the magical creature, his lower body seems to wade through the stone floor. Goodbark bounds after him, his fangs glowing.
SpoilerOOC: Moonwort casts tiger tooth on Goodbark as a swift action, wild shapes as a standard action then moves into the golems square. making an automatic trample attack if the creature is small enough. Treants do double damage against objects. Goodbark will charge.
http://www.d20srd.org/srd/monsters/treant.htm
I can write up the stats for Moonwort as an treant if you want? Barkskin spell and natural armour bonus as a treant seem to stack. (lol)