LOL, tried my luck in the Zertinan Caverns, I wanted to go after the Esper Adrammelch..... Well, I started to put a nice hole in his HP, until the other guys around him started to appear (roughly 3,000HP each) and they attack strong.
Summoned Belias, and he was doing well, but his low HP and Ashe's (she has Belias) lack of MP after summoning, caused her to not be able to heal quickly enough, and Belias was KO'd.
I will try again soon, but just arrived at the Henne Mines. After the Mines, I'll give Adrammelch another go. He only has 39,630 HP. If I can get some strong Weapons and do 1,000+ attack, I'll be right.
I also knocked off a couple of Marks. One being the Level 5 White Mousse!!! This guy was hard, REAL hard!! Has 69,469 HP!!!! (hint, you want to have an easier chance, Summon Belias, and use Reflectfa Motes on Belias + character. Then, just attack and attack!! Sure, Waterga heals the White Mousse, but at only 300+ HP (or damage) the Pain Flare does close to 2,500 each rip!!
I think I summoned Belias 3 times (a lot of Ethers were used).
I also took out the Ring Wyrm. He was tough, but was able to get through him easily enough, it just took time (with 128, 648 HP, that says it all).