quote sum_dude

A horse chasing a giant boar the size of an elephant, wouldn't that look odd?

Um... We're talking about a game where a dude that grows horns and comes back to life 16 times takes down large stone/flesh beasts who can also sometimes shoot fire and electricity at you. And there's magical lizards that increase your strength...

Yes, I've already taken that into consideration. Obviously, #11 and #14 are very, very aggressive. So, we can assume the same for the boar. Even more, boars are naturally aggressive. As for #13, the sky serpent, not so much, so it makes sense that you can ride up beside it and hop on. The the boar would most likely being chasing you around, being territorial. If you rode beside it, it would probably attack you before you had the chance to jump on, and I don't think it would be fitting to have Agro attacked like that running at full speed just for you to have a chance to jump on the boar. My point is that the boar chasing you makes more sense than it just running around aimlessly not attacking you while you're right next to it preparing to attack. Is that clear enough?

What if it was a really nice pig?

I really doubt this is how a nice pig would look.

By the way, here is where I got it from. The one pictured is unofficially called the rhino but I'm assuming its the boar.

Going back a little bit here,

quote reaver11

I couldn't even imagine what this game would be like in HD

We could probably get people to believe that it already is HD. It's that detailed, except for the little bit of fuzziness in the detailed stone (that can be almost completely fixed by lowering the sharpness on your TV's settings).

i would say yes make a part 2!
just make a new story.
i want to kill more huge bosses!

That's a good idea. Make another game, design a few more colossi to go with the ones that didn't make it into this game, and have the story occur completely separate from the original game and Ico.