This is simply and idea since I have no experience coding whatsoever, however I'm willing to learn even though this idea seems VERY ambitious.
My goal is to create the game mechanics of SOTC into Minecraft. I'm just not sure how the whole climbable entity thing would work. If that's even remotely feasible. I wouldn't want to directly copy the colossi into MC. I'd rather make up colossi that integrate key elements from MC into them instead. Like a nether colossus or an ender colossus. Stuff that would make since. Addon colossi for mods like AetherII and Twilight Forest would also be on the bucket list. I was thinking incorporating minions into the colossi somehow just to add an extra hazard while climbing. With that, you'd be able to maybe shoot a crossbow while climbing a colossus. Spawn the colossi throughout the world with a structure based on their respected element.
That's as far as I've got. Sound pretty gnarly, right? I just wanted to pitch the idea and see how possible something like this would be.