What is the easiest way to defeat two Hewdraw heads at once?

To unlock a panel, I need to defeat two of the Hewdraw heads at once on any intensity. I have tried a few times already, and it seems that wearing two heads down and using an ultimate attack doesn't defeat them. Has anyone done this yet, or do you have an idea, weapon type I should use or strategy to do this?

I played the level on 0.0 difficulty. I used a Knuckle Staff (Most staves will probably do the trick though), then I just fired off both special attack orbs once he was targetable.

Once I used the attacks, it knocked both heads off. Not too hard at 0.0 difficulty.

On 0.0 intensity, use any club or staff weapon's special (power) attack by tapping the one of the two blue orbs at the bottom touchscreen (they regenerate after use). This attack will damage all three heads.

Three or so should be enough. You can hit each head with a charged attack and then use two special attacks.

Wow. I just played the level, and found out that when you wait long enough, Lady Palutena says she is charging an attack and Pit says he can defeat the three heads himself. But if you wait longer, she will fire the shot and destroy all three heads at once!