It's not hard to get what you need and the battle will last about 3 minutes at the most.
------------------------------------------------------------------------
Spoiler
You'll need three spells to do it, and preferably either The Sword of Aeons are The Tear of Avo. You might also want to max out your Magical Energy as well as Physique, Health and Toughness. The three spells are Multi Strike (I had Multi Strike 1), Time Slow 4 and Berserk 3. When Jack lands, use all three of these spells. I was doing 1840 (!!) damage per strike and that was just with Multi Strike 1. If you avoid his attacks, you can kill Jack before he ever takes flight.
-------------------------------------------------------------------------
If done right (shouldn't be too hard), you won't even need to use a Health potion.
The final boss is really easy anyway. all you need is maxed out berserk and maxed slow time and you can take him out the first time he comes down for a landing.
When in doubt...kick it
Word to the wise, published opinions aren't facts, for those who can't tell the difference.
All bosses in the game are easy, I never died... And yes, the slow time spell is awesome but I try to use it as less as possible because it takes all the fun away from battles. Your enemies just become frozen and can't resist (except for blocking)... As for the final boss, yeah just ping away with multiarrow and a decent ranged weapon. I was using arkens crossbow, even though bows are better due to the reload time it was better to use Arkens crossbow against a single enemy.
