Games : Strategies for beating Pumpking as a Mage?

I'm playing through Terraria using nothing but magic weapons, and I'm having a really difficult time with the end-game events (I have defeated all of the single bosses, with the exception of Duke Fishron). Virtually all of the ideal mage builds I see on the internet involve the Bat Scepter, which is dropped by the Pumpking. But, no matter what weapon combinations I try, I just can't seem to beat the Pumpking using magic weapons.

Are there any particular strategies for taking him down as a mage? I've built an arena with traps, I'm using the Spectre armor (with hood), and I'm using a Nimbus Rod, Rainbow gun, and Heat Ray. I can wade through the first few waves in the Pumpkin Moon event (up to wave 9 or so, albeit dying many times), but I just can't bring down the Pumpking.