Defeat 11th Colossus
As soon as the battle begins run to one of the altars and climb it. The colossus will charge into the altar, knocking loose a wooden stick. Hop down, grab the stick, then climb the altar again. Press O to light the stick on fire. Because the colossus fears fire, you can use this stick to slowly force the beast off the edge of the cliff. The fall will break its armor, so jump down on top of the beast and stab away.
Defeat 12th Colossus
Begin by swimming around to the back of the colossus. If you’re having trouble, go under the armpit. From the tail you can climb onto the beast’s head. Hit your sword against the external teeth in order to ‘steer’ the colossus towards one of the structures. When you’re close enough, leap to the top of the structure. The colossus should eventually climb the structure; use this opportunity to leap onto its belly and stab the weak point. You’ll have to repeat this process at least once.
Signs in the Sky
Defeat 13th Colossus
Shoot the three white gas sacs, then ride up alongside the colossus while it’s low to the ground and leap from Agro onto the wing. You may have to repeat the procedure up to three times in order to stab all three weak points along the spine.
Defeat 14th Colossus
The trick is to move from pillar to pillar. Use your arrows to goad the colossus into knocking down the pillar you’re standing on, which will grant you access to the next one. Continue platforming around the area until you reach an area with a weak second floor. Get onto this floor and use your arrows to coax the colossus into charging the support columns. The floor will collapse and break the beast’s armor. Jump onto its back and stab away.