Shadow of the Colossus/Valus - Colossus 1

The first Colossus that you encounter is often called the Minotaur, but his proper name is Valus. With broken horns and fur primarily over the torso, this club wielding giant will roam an upper valley east of the temple.

The Colossus has two weak points. The first is on the very top of his head, and is where you will do the most damage that you can to the beast. The second is on the back of the left leg, which when struck will cause the Colossus to fall to his knees, allowing you time to clamber up onto his back.

The most direct means by which to defeat this Colossus, the easiest, is to catch a hold of the furry part of the back of the left foot area. Be careful, though, as the slightest step of the foot touching on the ground can cause damage to you, and send you tumbling due to the tremor generated.

Once you're on the Achilles heel area climb up to the weak spot and stab it with your sword a few times. Valus will then roar in pain, fall over onto his knees and subsequently get back up.

Sometimes it takes more than one knocking over in order to get up onto his back. Across the back of the Colossus are platforms, each one capable of being used as a resting point to recover your stamina. However, one must be careful if they decide to rest on them, since the colossus will shake its back in an attempt to knock you off. If this happens, you'll either need to hold R1 and hope you catch the platform's edge or jump up and grab some fur. If you fall you'll have to start all over again.

When you're ready, continue your trek up Valus' back to the top of its head. Once you are there, whip out your sword, situate yourself atop the thrashing head, and stab his brain meats until he dies. If you start running low on stamina just try to either get onto his upper back or shoulders, or even onto the platform closest to where you are. In terms of difficulty, Valus is one of the easiest, once you understand how to get onto his back.

Hard Mode Strategy
On Hard Mode, Valus doesn't die after being stabbed in the head. Instead his weakspot disappears and you'll need to find the next weakpoint. This won't be too hard though, since you probably noticed the glowing point while scaling the beast. If not, it can be found on his right arm (the one holding the club). Getting on to his arm takes a small leap of faith; literally. Drop down onto the upper platform on the right. Next run and jump of the edge, quickly pressing R1 to catch the fur as you fall. It's not a hard jump, so with any luck you will end up near his brightly shining weakpoint. Charge up the sword and stab away once more. Unfortunately, the hero's isn't that great, so there's a chance you;ll fall before finishing off Valus. If that happens, simply repeat the steps you used to get on him and continue until he falls.