Depths/Stage definitely has some variance to it, both in terms of whether you assemble the combo in a timely manner as well as whether the opponent has the best answers. The metagame presence of good answers, as well as the overall speed of the metagame are major factors in determining whether Stage/Depths is a good option.
However, most decks rely on mulligans to find graveyard hate, and Bazaar can be used to dig for the combo, so Stage/Depths is a much more attractive sideboard plan for Dredge than it might be in a more dedicated deck like Dark Times. It can be a "bad" option in terms of metagame and still score quite well simply because it is hard for opponents to answer disruption, dredge, and depths all consistently.
I think the best answers to Marit Lage are not being played quite as much right now as they have been for a while. What do you think of the following? (post-London)
4 Bazaar of Baghdad
2 Serum Powder
4 Golgari Grave-Troll
4 Stinkweed Imp
4 Golgari Thug
4 Cabal Therapy
4 Bridge from Below
4 Hogaak, Arisen Necropolis
4 Force of Will
4 Force of Negation
2 Mindbreak Trap
4 Petrified Field
4 Mental Misstep
4 Dark Depths
4 Urborg, Tomb of Yawgmoth
4 Thespian's Stage
2 Vampire Hexmage
1 Riftstone Portal
Hey that's weird... it looks like you don't have a lot of ways to activate your own Death's Shadow - it seems like most decks could play around them if they knew and wanted to. Is that a potential issue in your view?
(But obviously congrats dude that's an awesome result)
Can someone do the math on effective hand size treating Powder as a blank?
If I keep half a card more on average but I also keep a Powder half the time it starts to look like not so much of a benefit
There's a reason normal decks like Workshops don't usually run Serum Powder even though they would also like to keep a larger hand.
Edit: And of course you have to include the odds of drawing Powder in the first few draws.
5 is a lot of manas. I get that they're all Shops-friendly mana, but it seems like if this was strategically strong we would be seeing more Expedition Map currently. It seems like this would be most playable if you have some way to bounce or recur it, so you can get a stream of Strip/Waste effects (in addition to whatever utility lands and further Factories / Shops / etc)
I value Therapy much more highly than you do, Bloodghast much more lowly, and I think Therapy + Narco is a generally faster way of accomplishing the same thing as Bloodghast in that configuration.
The other issue is Dakmor Salvage, which is either taking up more slots or decreasing your average dredge (or both).
I think the Bloodghast/Ichorid/Hogaak/Bridge configuration would be a fine thing to test but I'm not particularly drawn to it.
Edit: Can we map out the other alternative? I think it was cutting Dread Return from a traditional package
Edit 2: Just to clarify, when I say I value Therapy more highly I'm saying I think it has a disruptive effect from the graveyard as well as being a sacrifice outlet from the graveyard. This makes me reluctant to cut it for a disruptive card from the hand which has no particular graveyard synergy.
My concern is that without Bridge it's harder to chain together multiple Dread Return, but I think it's more something to be ironed out with testing / tweaking than a real objection to the whole archetype.
So I think this whole no-Bridge DR thing is workable, but I don't see it saving slots for more disruption.
Is there another list I should be thinking about that saves more slots?