What level should this vestige be?

[The Shadowmind]

Make that stun thing mind-affecting, spell out what condition it forces on the creature and usable once every five rounds and I would say it´s a strong 6th level vestige.

IIRC it would also be the only vestige with two 1/5 rounds abilities.

Zceryll also has 2 1/5 round abilities. That is a webmaterial vestige though.