*your sword drives in enough to stick, and the colossus thrashes even more fervently, but you manage to reach down and bring the shadow's hand up to the sword hilt and cover it with yours. Thus braced, you can both wait safely -- dizziness aside -- until the monster grows bored of shaking, and begins to lumber forward again.
Your arms are trembling with fatigue by the time you haul yourself up onto the colossus's shoulder, and the shadow seems exhausted. Once there, however, you can rest a moment, if you're careful and think you can risk it.
Stone ridges encircle the monster's head, spreading back from its face, which seems to be made entirely of stone. It should be an easy climb to the top of its head, if it cooperates.*