The Stone Golems are defeated within ten seconds if you're wearing the Dragon Armor, which is why I think they're the easiest. The Pumpkin King is also very easy to defeat and so are the Guardians of the Graveyard.
The stone golems. Just put on the dragon armor and knock them off the castle edge using the flame. Easy.
All bow down before the master of the vegetable patch, the prize-winning plant who can summon an army of cabbage with a wave of his noble tendril.
He's delicious. He's nutritious. He's Zarok's secret recipe - he's the Pumpkin King!