The Ice Titan has 3 patterns and each require a different but similar way to hurt him.
The only way to hurt the Ice Titan is to hit his shards back to him*. The Ice Titan has 3 attacks in attacks in the beginning of the fight. First, is his basic “always-facing you” shockwaves which have low range and are only made to prevent you from coming close to him for free hits. Obviously, stay away from these waves; they only are brought out as you circle the Ice Titan, because the Ice Titan will always face you (sort of a lock-on to you). Second, is his slagamite/ground-icicles that follow you. In order to dodge these, you must either run in a circle (not back and forth) or just glide around until the attack stops. His third attack is his most important is the only way you can hurt the Ice Titan. This attack consists of a bunch of homing shards that come towards Sora in different ways. You must hit the shards back to the Ice Titan in order to damage him.
* LEAVE AP ABILITY VORTEX OFF
Now, the best way to hit these shards is to short-hop jump hit them. The shards come in 2 different ways: A string of 5 straight shards right at you and a 3-wave attack of 5-spreaded icicles that are separated. Short hop jump hit them and you should hit him enough to get to his first stun point. The first stun point is about 75% through the first HP bar, once you see a flash, glide in and do as much damage as you can!
Part 2 starts off with the Ice Titan shooting a barrage of shards right at you in which you must get ready to swing with all your might (about 3 times you can go 4 though it is risky). Now, a difference between this “form” and the last is as you move around the Ice Titan he will shoot his shards at you, rather than you waiting for him to face you. First, let’s talk about his two new attacks: A- His Ice Breath and B- His Ice Boulders. For the Ice Breath, you just need to dodge roll or glide out of there. The attack comes out slow, but it can freeze you and do a good amount of damage, in addition to freezing the floor (which Sora will slip and leave you vunerable to attacks).
GREAT HINT at 2:50 (specificlaly 3:20) in the video to help those who can’t hit the shards.
For the worded way: Sora grips the Keyblade right handed but he has a left-handed swing. So, you want to place Sora at the right side of every shard coming at you in order to consistently hit 1-2 shards per time. THIS ONLY WORKS FOR THE SECOND FORM.
Sooner or later he will stun bringing us to his 3rd and final form!
The final form has similar attack patterns to the first form but with a major difference. The final new attack the Ice Titan uses his an infinite trail of Ice Boulders, rather than the shards of Icicles coming or nothing at all. So, as you circle around the Ice Titan and/or he is not facing you, you must be dodging the Ice Boulders!
Now a hint for the Ice Boulders it TO NEVER JUMP! Jumping will only allow them to spawn on you and just make you lose damage. What I recommend is to run in a circle while you wait for the Titan to face you! This way, you will not have the boulders spawn infinitely and you can save a lot of time! The shards come in the same pattern as the first form and you just have to stick with it!
Remember to heal (at perfect timing with boulders to not get hurt) and hit as many shards as you can back!