Maybe if he swung the pumpkin once like a mace infront of him, then a spirit fire in the shape of a pumpkin flew out to stun the enemy. When the fire is out, the pumpkin goes dim.

Then near the end of the animation for stun, the fire on the pumpkin flickers back to light.

I feel this is better than the pumpkin just suddenly appearing in his hand again.

As for the stun particles of the pumpkin explosion, just add a more burning kind of effect to the chunks of pumpkin pieces.