Basically what the thread title says.
1. Mobility. This is what made me quit my aran in the first place. Always needing to spam the right arrow key to dash is annoying. Same goes to mech.Besides, mobility is important for dodging skills that can 1HKO, like cyg's dark genesis.
2. Status Resist. Now when I look back at my captain, status resist is a must in bossing as otherwise I can die easily due to sed + when my HW is on cd.
3. Avoid. I won't deny, this is an important part of bossing. Skills like Xenon's DBD and DB's ShadowMeld increases avoid to a rate until the boss can't damage them (inb4 AoE attack lol)
Other parts (minor)
Class (Pirates ftw, but I refuse to make a mech)