If pure-blooded Garleans can't use magic...

[Anonymoose]

Any answers/theories? :O

There are two things to look at to make a guess - the color shift in his armor, and the attacks he uses in the fight.

Golden Armor
When the shift occurs, he draws Heirsbane and electricity crackles around him before exploding outwards in a golden flame that seems to change the material of his armor. When Ultima begins to fall apart, an explosion in the cockpit blasts him out of the back of it and, as he lands on the ground, another golden electrical explosion is seen and his armor reverts to black. At first, I had assumed that this was due to his alliance with Lahabrea - that the Ascian had given him a little oomph, the way "Almighty Dalamud" had "gifted" some magickal power to Nael van Darnus. Now, I'm not so sure. Baelsar doesn't seem to think twice about it and seems pretty confident in magitek. The mount guide says that some magitek are gilded to dampen magickal attacks against them - perhaps Baelsar's armor has some type of small, magitek device that temporarily gilds his armor in battle against those who can wield magicks against him.

Battle Abilities
Most of his attacks are either related to his swordsmanship or with blue flames. Blue flame is the result of ceruleum, an unstable fuel used to power Magitek and weaponry, so, really, none if his attacks may be magickal in nature at all. The flying blue X is the most likely culprit (aside from the Super Saiyan Steel), and even that might just be flourished ceruleum-infused swordsmanship.

It's Ninjutsu!

Ninjutsu is a form of magick.

In one of the 1.0 cutscenes, Nael moves so quickly it looks like he's teleporting. I assume Gaius is capable of the same thing since they're about as powerful as each other.

Darnus definitely had magick as a result of his connection with Bahamut. Gaius, it's possible, due to his association with Lahabrea, but I find it less likely than the animation team getting really into the potential of magitek.