I'll try to put out a lot of points here..
- Bolt is effective. (Beating Paarl first for the paper is recommended if you want this advantage )
- At Rom's first position. Eliminate all the spiderlings. Then charge r2 Rom atleast twice. Before reaching 1/4 damage on his HP. Make sure you have full stamina to pour all out on Rom. Usually after the first position you'll find Rom teleporting to his last position rather than the 2nd.
- When he raises half of his body, run sidewards to avoid the ice meteors.
- When he lies on his back, there are patterns of the meteors erupting from the ground. Or you can just run away.
- When he charges up, either you dodge it or run for it. If you think you'll get hit, do not try to dodge or heal; you'll get less damage if you don't.
- As for trying to avoid the spiderlings in his last position. Just pull some running R1s with an additional R1 then run away again. Find an opening ( heavily dependent on what weapon you are using, but works well tho based on my experience ).
- When he thrashes around ( usually happens right after you hit him ), just dodge AWAY from him.
- Don't heal when you are near him or his spiderlings. When I first fought him I only heal when I see him make a move and I've covered a good distance.
- Use the student uniform set or the Executioner Set. They have great arcane defense stats.
I'm not sure if I missed some or if these could help you, good hunter.