Having had a quick scout on the Internet for suggestions as to how to defeat the daemons in this tower, I found that the best was was by using:
- 3 x Wind-up Lord Vexxos
- The ascension slot of 'Ultimate Powercraft' at 999 AP
- Having crafted spells of 99 of one element and 49 of another
- Eating Lasagna al Forno
Well, #3 and #4 are certainly fine. Nothing difficult there.
As for #1, that was easy. You need to go to Altissa and use the right-most arcade game which costs 10,000 Gil per game. You'll find it where you can meet Alessio. There is nothing difficult about playing this game, it's just a matter of patience as you need 99 gold bars (and they seem to be rewarded randomly) to obtain 1 Wind up Lord Vexxos. That done, my biggest challenge was #3 - how to get enough AP fast!
Here's a really easy way. Head to Hammerhead and park up there. Walk into the wasteland behind it and you'll see some Sabertusks running around. Use your best weapon to warp-kill them all (I dropped all other parties' weapons down to their most basic to give me the best chance to kill all enemies - although even their lowest level weapons will kill in one strike). These beasts are only Level 2 and spawn at 3 to 5 at a time. Using the 'Summon Enemies' whistle, just stay in that spot and repeatedly call enemies. You'll end up with Sabertusks or Reapertails. All easily despatched. This way, in one Final Fantasy day (6am - 8pm) you can earn around 300 AP. Back to Hammerhead and rest and do the same again for another 2 days or so and you've got your 999 AP to get this final magic ascension.