more ideas:
Claustrophobia/Paralysing Grasp (lets me get 2-for-1s out of bestow)
Sensory Deprivation (cheap as hell and shuts down a dude)
Hired Torturer (blocks, provides a clock + information)
Contaminated Ground (fucks up Guildgates and occasionally hurts people)
Death's Approach (a better Viper's Kiss in some matchups?)
Mortus Strider (probably wouldn't do enough, but it's interesting)
Quag Sickness (probably not powerful enough?  Unlikely to be better than Stab Wound, that's for sure)
Deathcult Rogue (both a 2-life clock and two devotion for Gary, but doesn't really affect the board outside of that)
Perilous Shadow (oh hell yes)
Murmuring Phantasm (it's cheap and blocks)
Omenspeaker (also cheap, blocks [although dies to Lightning Strike] and actually has both a relevant power and a really good ETB as well as being useful insurance against random Viashino Firstblades - I want these main deck but I don't know what to take out for them)
Balustrade Spy (to attack evasively for 2 and contribute to my Secret Tech (tm) in the mirror or other slow, grindy matches after they board out spot removal - probably not worth it, but he's an option, as are Vaporkin and Deathcult Rogue if I expect people to board out their Pharika's Cures)
Runner's Bane (don't think it's as good as Sensory Deprivation by a long shot, but it exists)
Shrivel (vs. Akroan Crusader and mono-red in general)

Thoughts:
- Disciple of Phenax is pretty bad against aggro.  Probably worth siding them out in that matchup.  Maybe in favour of more Viper's Kisses, Omenspeakers, and maybe Perilous Shadow - it's the magic Toughness 4 and actually kills them/their stuff once you untap.
- Lifegain is going to be a thing.  Gray Merchant and Hopeful Eidolon mean opponents will be gaining enough life that I can't rely on winning through Stab Wound, Gary and random Benthic Giants alone.  I think Perilous Shadow (again) is the answer.  He's an amazing blocker - even deals with the likes of Rumbling Baloth/Nessian Asp + Hopeful Eidolon - and later on, once my opponent's topdecking, attacks for 6 like a total boss.
- Flying (Nimbus Naiad mainly) and Aqueous Form may be an issue.  Given the many ways in which an opponent can do horrible things when I don't have Grisly Spectacle in hand, a second heavy duty removal spell is essential.  Claustrophobia/Paralysing Grasp are sorcery speed, but they're quite cheap (letting me cast them turn 5 or 6 and hold up Essence Scatter or Pharika's Cure) and have the tremendous benefit of sidestepping bestow's annoying ability to act like a 2-for-1 against removal.  Negate and Disciple of Phenax also work against these strategies, but I like Claustrophobia the most just because of its raw card advantage in this situation.  Nom.
- Devour Flesh is awesomesauce, but doesn't work with Stab Wound.  There may be matchups where I side one out for the other, in which case I can run it, but otherwise I'd prefer Stab Wound - it's precise and does a great job of blunting monsters or killing smaller creatures.  The life drain even helps me race if I have a decent enough board position relative to my opponent.  Plus, Stab Wound on a Deathbellow Raider is the funniest thing ever.
- Do I run a 25th land?