Where do I find the spell reverse and renew?

Renew can be purchased from the merchant in the Dalmasca Westersand after the events in the Pharos At Ridorana and Reverse can be purchased from the Muthru Bazaar.

That is the esper Zalera the death esper. There is nothing you can do about it's kill ability you'll just have to revive any character that is hit with it and try to beat it as fast as you can. When he summons enemeies to help him kill them quickly because Zalera gets a defense boost when they're there. There are times during the battle where your attacks won't affect Zalera here so instead you can use techniques like a 1000 needles.

Attack it.

Renew can be obtained in the Dalmasca westersand after you've played through the Pharos at The Ridorana Cataract and reverse can be obtained from the Muthru Bazaar when you reach a certain clan level.
To Beat Zalera spam Curaja/Curaga at it and He'll go down pretty easy. =]

Reverse can be found in the clan shop once you reach a certain clan rank.

Renew can be found in the Dalmasca Westersand, use a Gate Crystal.

The boss there is called Zalera, an Esper. I'm not completely sure how to beat it though. That's the next Esper on my list though.

Hope I helped,
7OneWingedAngel7

zelera is easily killed if u just use cure spells on him such as renew and curaja

If you still need help on zalera: heres the easiest strategy...... Casdt reflect on everyone and spam curaja, it'll sttack zalera massively. Not heal him