I'm curious to hear how the Ghostly Prisons perform for you. I considered them for my martyr list (Martyr Proc) but decided not to include them.

I never considered Hex Parasite, but it seems a little too narrow to me. I definitely don't think I'd play 2, because I don't think you need more than 1 with Ranger of Eos to grab it. You should consider running a Walking Ballista. It's also decent against planeswalkers, and I've found it to be very good against stuff like Lingering Souls, Young Pyromancer, and Dark Confidant.

cstick,

I don't have a ton of experience with the deck yet, and Ghostly Prison is very much a meta-call, but I've found them to be ...

• Amazing vs. go-wide or go-big decks that don't have a ton of mana available (e.g., Humans, Affinity, Bogles, Pyromancer, Death and Taxes, Merfolk, 8-Whack). A Prison or two and some chump-blockers can usually stop them cold.
• Good vs. decks with a "fair" amount of mana (e.g., Hollow One, Jund, RG Eldrazi). A Prison or two will slow them down but never stop them ... but sometimes that extra Turn or two is all we need.
• Kind of indifferent vs. Control. Generally useless, though they can prevent Snapcaster beats for a little while (until they get enough mana to attack and hold up counter-magic).
• Completely useless vs. Combo (any of them) and decks with tons of mana (e.g., Tron, Titan Breach, Elves, Mono-G Devotion).

I really like Hex Parasite. I could totally see adding a Walking Ballista to the main just because of its versatility, but IMO the Parasite is much better at killing Planeswalkers. E.g., it takes 8 Mana to kill a Liliana of the Veil on 4 Loyalty with a Ballista (and it kills the Ballista in the process), while it only takes 5 Mana with Parasite plus we get a 5/1 out of the deal. And yeah, 1x is almost certainly correct (FWIW, I've seen a bunch of competitive decklists with 1x but have never seen one with 2x), but I like having 2x ... partly so I have a better chance to draw one early rather than having to Ranger one up, and partly so I've got another available after the first one gets killed.

Thanks tons for the thoughts; I'll check out your deck shortly!