Agility

[Kamrusepas]

Which monster in the Arena will give you Agility Spheres?
If any?

[alexholker]

The unlocked wolf (Fenrir?).

[rubah]

fenrir.

Better up your accuracy/speed first, because that sucker likes to kill stuff.

until you're faster than he is and/or have death immunity

[edit-- stupid, stupid, forgot agility=speed. Instead, maybe have the magus sisters kill him if you can't. but hopefully you can, because having them do ANYTHING gets to be a bit annoying]

[Kamrusepas]

Does it help if five of my chars hit 99,999 and have HP of 30-45 000? :P

[rubah]

Sure it does It always helps ^_^

[Chopseuy]

My characters had 40000 Hp+ (Auron, Tidus, Yuna) with almost the entirely Sphere Grid completed. I killed all the monsters in the arena, including Shinryu (this was tough because my Rikku was weak as hell) and Nemesis (after a dozen billion tries).

For Fenrir, you do need speed. Use Tidus, a must, and Wakka. Yuna should always be in the party, so she can help you out with healing, and summon Magus Sisters when things get rough.

[Kamrusepas]

Hm, first of all, my Yuna sucks 'cause I haven't developed her that much.
Second, I don't have Magus Sisters... Nor Anima...
But I'll try. Can't be that hard..

[alexholker]

IMO, the two most important things to have are:

Confuseproof/Ribbon armours for everyone who will be in the fight.
High Evasion (Kill Pterix if you need Evasion spheres).

Don't bother summoning Aeons, as Fenrir has an attack which insta-kills Aeons. Apart from that, it has two attacks - one which does Demi-like damage and Confuse, and one that causes Death. The first attack can never actually kill you, and if you are Confuseproofed, you don't have to worry about it at all. The other attack is easy to dodge if your Evasion is high enough.