Crit Damage + Damage proc.
He desperately needs damage proc for skill 5th to blow everything on its path.
Don't even think about invincibility for PvP because he can't stand a chance against any PvP meta.
General wisdom on obelisks is to get one with proc damage (PvE) or invincibility (for PvP). Get GBI if using him on auto-play in timeline or for AC. As for the other stats, HP boost or crit rate/crit damage is preferable or ignore defense if you’re low there. IM doesn’t do elemental damage (afaik) so those boosts aren’t needed.