To get Mascot the last episode HAS to be Mt. Gagazet. And yes, you have to go into Bevelle and talk to all 3 brothers: Isaaru, Pacce and Maroda.
To beat Angra Manyu you can start hitting in on your digs on Western Bikanel since chapter 2. Just don't dig the yellow X, it messes up your completion at Djose temple. Before chapter 5 Angra fights just a couple of rounds then he throws you away, but you can steal a Megaeleixir from him before that (ME healls all HP and MP of your entire party. Pretty handy to have later). The best part is that Angra never heals so when you face him on chapter 5 his HP will be a lot lower than facing a "fresh" Angra Manyou.

You can always use the Catnip and Trigger happy trick...