Auriok Champion is pretty tough to deal with (Engineered Explosives or ambushing it with a Snapcaster Mage if it dares to attack are probably your best bets on that front), but Leylines don't strike me as especially bothersome. You should be able to fend Dredge off long enough with postboard Angers and Surgicals to find your Shadow and muscle through them.
I'm still on Looting. I tried playing without it for a time, and I was displeased with the results. A sneaky thing about GDS is that some of your cards become dead in the mid-to-late game (life total dips too low, run out of fetchable lands, etc.), and Looting can help you cash those cards in for gas.
Bauble is good in that it lets you really drill down on the land count. I'd have to play at least 1 more land if I didn't have it.
The 17-land lists I saw when I was building up the list weren't cutting the 2nd Crypt. Instead, they lowered the fetch count from 12 to 10. I feel like 10 fetches is the way to go - I don't really want more.
I've been treating Hollow One much like any other creature deck - they're heavily geared toward dealing damage to us, so you can cut down on the things on that we use to damage ourselves (Street Wraith and Thoughtseize) and just stuff the deck full of removal (Abrade and Kommand in particular, as they can take down a Hollow One). Toss in some Surgicals to keep the Bloodghasts and Phoenixes off your back, and you're good to go. It's been pretty successful for me so far, but I will grant that my reps with the deck are still somewhat limited.
I'm in the market for a backup deck to my Merfolk, and I'm looking to work my way through a few options. Grixis initially caught my eye because of the highly interactive playstyle, and because it seems to have the tools to handle decks that are bad matchups for Merfolk, such as Affinity and Lantern. Here's a 75 I've put together based on some testing and some looks at the top lists:
I know that Bolt is a somewhat unpopular choice of late, but I think they're handy. I don't like the notion of being cold to random Mirran Crusaders, and Bolt-Snap-Bolt is always a nice bit of reach. I suppose there's an argument to be made for running Temur Battle Rage over it, but I'm still uncertain of how much I like that (which is part of the reason I'm here). As of now, the cards that I'm debating whether I should include or not are the Battle Rage, Liliana, the Last Hope, and Engineered Explosives. Opinions on those cards, any other cards I might be missing, or the list in general welcome.
I honestly can't fathom wanting to even trim Snapcaster Mage in this deck. It fits amazingly well. I can't imagine a metagame context that has me thinking "maybe I should shave some Snappies." It'd have to be something absurd, like 20+% of decks packing Rest in Peace mainboard (at which point Snapcaster's not the only thing that looks bad).
I'm out on Temur Battle Rage as well - you need something like a Shadow that's 6/6 or greater to really get any juice out of it, and I'd rather not have a card that's completely dead until then. The Lightning Bolt vs. Terminate discussion is an interesting one. It's still hard for me to fathom having Snapcaster Mage and less than 4 Bolts in a Grixis deck, but that may be a holdover way of thinking. I still like having a bit of reach for when the opponent gums up the ground, but I will test with an eye toward how often I use the Bolt to close out games as opposed to removal.
I'm still trying to feel out the land count. 18 has felt like a lot at times. The deck just sees so many cards in a typical game that any more than 18 feels unnecessary. I could see shaving a Bolt (or two) for Terminate in order to make room for sweepers, though.
I think FlyingDelver is right on that front. The only matchup where Street Wraith should ever be considered as a potential cut is Burn. And since I'm here, I thought I'd run my current list by you all and get your thoughts on it: