How do you defeat Riku the 2nd time on Kingdom Hearts

You need something, what is it called?
um.... Oh yeah, you need Ars Arcanum.
heres a guide to do it.
Sora will have to do this one on his own, because Donald and Goofy
will be blocked off by force fields. This means you can't use
summon spells. The only spell that you should cast is AERO. Rely
on items (ELIXIRS) rather than CURA. Now, how to beat Riku. Well,
first of all, he is fast. You won't get any breaks. Use Guard to
deflect his basic sword slashes and earn 17 Tech Points. This won't
stun him, however. Ars Arcanum is an essential part of your
strategy, but you can't use it foolishly. The only time Riku is
actually vulnerable is when he holds his Keyblade in front of him,
and says something like "Is that the best you can do", or "Show me
what you've got" or "Come on". Your first hit will knock his weapon
back, and then you can continue hitting him for a combo. This is
the best time to unleash Ars Arcanum, as Riku will be able taste
every ounce of it. You won't miss him. After awhile, he will start
glowing. He then tosses projectiles at you. Do your best to repel
them with Guard. He also jumps into the air, and slams his sword
into the ground, causing energy pillars to appear. You can avoid
these pretty easily if you just keep moving, paying attention to
where the pillars are rising from. When about a quarter of his
green health meter is depleted, Riku will glow again, and this time,
he will teleport around the room. Glide during this attack, but
don't expect to come out of it completely unscathed. Afterwards,
the battle will go into overdrive. Guard and Glide when necessary,
and use Ars Arcanum if you get the chance. This is the home
stretch, so keep an eye on your HP. It would be a shame to die now
-Mikeman97