Shadow of the Colossus/Argus - Colossus 15

The fifteenth colossus, Argus, is a huge giant, with a huge club to go along with it. To get to him, go north to where you fought a previous colossi, and then head east to the large castle. You can't take Agro with you into this battle, so dismount and head in on foot. When you get to the ground in between two large walls, keep heading forward until you get near the edge of the cliff. Once you get close enough, Argus will climb up, and begin the battle.

The trick to beating him is to get high up to the top of the walls either side of the arena. Lead Argus to the tiles beneath the shortest wall sections on either side. Stand on them, and eventually he'll lift his leg to try and stamp on you. Move out the way quickly, and the tile tilts. You can use it to jump up and grab the ledge. Climb the stairs. Now, pull out your bow and arrow and shoot the furry sections around his shoulders to provoke him. He'll swing his club-sword at the walls, causing blocks to fall. Climb up these to reach the next tier of the temple. At the very top, there are bridges leading across the arena.

Get onto one of these bridges, but don't go near the middle; stay near the walls. Use an arrow or two to get Argus' attention, and he will break the bridge with his club-sword. Whilst he's bringing his weapon back, you can jump from the remaining section of bridge to his head, where there's a glowing weak point. You won't necessarily get time to get a fully-charged stab in; Argus shakes a lot. Once the symbol on his head is gone head down to the arm that's holding his club-sword and you will see blue light on a particular section. Hit that and he will drop his club, revealing the vital on his hand. Drop down to the ground.

Instead of attacking you with his club, since you disarmed him, he will now try and pound you with his fist. Wait until he's about to bring his hand down, and move to one side to avoid it. It's only briefly, but his hand will get stuck in the ground, and you will be able to see the glowing weak point. Quickly jump onto it and hold on. The moment it's relatively stable, charge up a stab. You can finish him off with one hit. Argus will fall, and now, only one more colossus stands in your way.

Hard Mode
You will find the final weak point on the left side(your right) of his chest. Jump onto his head and climb down his fur to reach the final point and bring down the Colossi.