Well, I did think we'd did some other symbionts in a simplified way, but I can't remember which they were. :/
I vaguely remember doing a Hazard as a pseudo-symbiont but think it was a homebrew.
Let's go with Aberration (extraplanar) with something in the symbiosis that they can't be banished when bonded with a host. SNIP I'd drop Advancement.
Works for me.
UNSNIP Sleepless can probably be combines with Constant Vigilance, right?
I'd be fine removing Sleepless from the ability descriptions if we have "immunity to sleep effects" in the SQ line and a mention in the Constant Vigilance description that it's why the creature is immune to sleep effects.
Updating Worry-Wart Working Draft.
I'm of two minds on the Dex. The eyestalks can move around, but these are pretty immobile. Maybe there's a better way of dealing with damage to them than giving them AC and putting their highest attribute in Dex. Wis should probably be highest if they're good at seeing stuff.
The Armour Class is for the Worry-Wart when it's flying about free, symbionts use their host's AC when attached:
Symbiont Traits said:A symbiont never takes damage from attacks directed at the host. Like a worn magic item, a symbiont is usually unaffected by spells that damage the host, but if the host rolls a 1 on its saving throw, the symbiont is one of the "items" that can be affected by the spell. A symbiont uses its host's base saving throw bonuses if they are better than its own.
The original monster's AC 0 is equivalent to AC 20 in 3E. Since it's fine-sized 8 points of that comes from its size adjustment so it has another +2 from some other source. Natural Armour seems unlikely and a +2 Dex bonus seems the most obvious solution, although I'd be willing to entertain arguments for another source such as deflection or insight.
I'd be willing to considering a higher Wisdom modifier but would be more inclined to give it a racial bonus to Spot and Search if we wish to increase its perceptive ability. The flavour text doesn't suggest it's that "wise" in the self-awareness and understanding sense.