Well, considering familiar does not have trapfinding so it cannot disarm traps. But it has +7 spot&listen, move silently +7, hide +8 and spellcraft +6 and ability detect magic at-will (and be invisible at-will) it is decent scout and definitely can see in darkness. Plus fly around 50'ft per round with good maneuverability. Also not sure but I heard they also have huge racial bonuses on stealth stuff.<br/><br/>Ofc it's a imp masquerading as tressym but I remember imp does not loose it spell-alike abilities and such in other form. Bonus also that it has telepathy so can report without flying back.<br/><br/>Edit; Double checked, Alternate Form (http://www.dandwiki.com/wiki/SRD:Alternate_Form) keeps all best traits of the Imp while getting tressym racial bonus and movement mode. Tressym have +8 balance and +4 hide&move silently racial bonuses. So above it has +11 hide&MS.