This boss is rather simple.
To attack 'Boss Lumbering Fool' you will need to press a series of buttons when prompted on-screen (any other attacks will not cause damage to 'Boss Lumbering Fool').
When you first enter the battle, hide behind one of the red pillars holding the roof up.
Stay behind it and when 'Boss Lumbering Fool' takes a swing at you, his giant sword will get stuck in the pillar making him vunerable enough for you to attack him.
As 'Boss Lumbering Fool' tries to pull his sword out of the pillar, jump onto his sword, and this is where you will have to press the correct combo of buttons when prompted to execute the attack.
Press the buttons in this sequence: (Y), (repeatedly tap A), (Y), (repeatedly tap A) then (X) to finish the combo.
When the attack has landed sucessfully, you and 'Boss Lumbering Fool' will fall through the floor into the room below.
Repeat the tactic above untill you defeat 'Boss Lumbering Fool'.
On the 'hard' difficulty i needed to land 3 attacks to defeat him, (the third attack finishing him off).