Its a level III mark that I didnt mean to fight just yet, but I was looking for the 2 parts to a windvayne for some merchant cat, and stumbled upon em. I did my quickenings, took off seriously like 1/20 of the things power bar. So it all came down to Belias who does like 2k damage each time, and other than the physical attacks(rake especially), wyrm doesnt do much damage(whenever he casts fira or fireball, Belias just absorbs it, and none of the status magic works either).......HOWEVER, you hafta summon duke at least 8-10. I had the mark at like 1/3 power left, but then the mugucker immobilized and killed everyone except Ashe(Vaan to but he was my getaway plan) which wouldnt have been that big of a problem(while Belthias was fighting I would just charge, heal myself, and Belthias if he needed it, and once the summon was about to run out, I would make sure to get 2 charges in so 1 ether would fill the mp back up). But then ONE fucking time, right after I have called in Belias, the mark is still targeting me and breaths me for a KO. Needless to say, I bounced out, and it was only a 30 sec trip the oger-yensa sandsea crystal where I decided to continue the storyline lol.