I can turn to murder of crows as listed in swarm entry (as I took swarm variant of a vampire alternative form which also includes my medium humanoid form as form list). But gaseous form I re-themed to be swarm of crows which occur when he is 0 HP. As swarm the swarm cannot attack but focus entirely fly somewhere where my char can reform itself after getting hit with attack which sends him to 0 HP (or -10 as 0 HP is for undead who get destroyed during that moment). Vampires retreat for a coffin to regenrate but I thinked storm cloud would count as such sanctuary.<br/><br/>Gaseous form is invulrenable to most harm done but it can be harmed if you can reach it. So I thinked someone who goes hit and destroy the swarm (target swarm with attack which works vs it) which is on low HP (hit through DR and FH and manage hit it's AC) kills off my demon prince for good.<br/><br/>If this is not okay then he has no gaseous form then.