When you've got a pole, dodge Ugh Zan's attacks until he suddenly stops shooting and walks to a random location in the arena. Soon afterwards, he's start wrestling with a sand worm. Now, fly up to his back and toss the pole into his back by hitting the fire key. You'll know you can do it when you see a red pole outline on his back.
After he wrestles the sand worm away, he'll turn to face you. However, because you stuck a pole in him, he'll be struck by lighting. This will do damage to him, stun him and temporarily shut down his regenerating abilities.
Stunned Ugh Zan
However, you don't have enough firepower to kill him before he recovers and starts regenerating his health again. What should you do then?
Your goal is to put enough poles on his back so that he'll be weak enough for a few charged up cannonballs to kill him. Generally, three to five are needed, depending on your skill level. To do this, you'll have to repeat what you did earlier to get a pole into his back.
When a lighting strike has taken at least more than half of his health down, get close to him and start spamming him with non-charged cannonballs. After a while, he'll die! You win!