Castle Attack is an episode of Venturian Battle.
Robert Jacob and Terrence have forged weaponry and are selling them to people who will fight off the savage trolls at King Venture's stronghold. Robert and Terrence grab some axes and ride a Mine Trolley to the fortress. King Venture welcomes the brothers, and Robert finds his six other brothers have joined the king's army. Robert finds some trolls approaching, and uses a catapult to launch rocks at the monsters, knocking their heads off. Terrence goes to another tower, and uses a catapult twice the size Robert is using, to launch kidney stones at the creatures. Tyler rides a horse onto the bridge and uses a lance to impale the trolls.
In addition to trolls, an army of skeleton warriors also approaches. They use the catapults to launch more pebbles and kill a few of the skeletons. Tyler continues lancing, and impales a few of the skeletons with the lance. A colossal army of skeletons approaches and is about to get in via the drawbridge, until it is closed, sending them falling into the molten rock and burning to crisps. Athansios gukgung to shoot a troll's head off. Terrence pulls out a pole axe, and uses it to chop down more trolls. The king stands up from his throne and grabs a halberd, and kills trolls and skeletons. A guy using a necronomicon is spotted riding a wyvern, and tells them that he summoned the skeletons. The eight brothers ride another dragon and the dragon bites the necronomicon wielder's head off and takes back the book of the head. Meanwhile, a black skeleton and a charred zombie are about to destroy the castle, but step on a booby trap which sends them falling off of the bridge and into some lava. Robert stores the book of the dead in a chest deep under the castle, but also encounters a dragon. Robert and his brothers, alongside the king and the knight general, ride the dragon through the castle. They eventually make it out, and the dragon flies through the sky, and eventually off of planet Venture entirely.