I just beat the dragon, though it took a little practice. The following steps should work:
1. When you get close to the dragon, use invuln potion.
2. When it wears off, teleport back.
3. Use a seed to grow a tree.
4. When you've destroyed the tree the potion cooldown will be gone, so repeat steps 1-3 untill dragon is dead.
It may take a little practice and I'd say you can do it easy with 4 of each invuln potions, seeds and teleports.