I think both of these are worth testing, but I haven't been able to play recently.

Here's a summary of the cards I've considered but have cut:

Imp's Mischief: This weird card is really swingy and fun to pull off, but annoying to play against. It also leads to players doing nothing if they suspect you have Imp's Mischief which isn't what I'm going for.
Dash Hopes: Only useful when the opponent has <= 5 life because otherwise they generally want to lose life.
Mana Tithe: This rotted in players' hands too often. The high amount of discard makes this worse because the opponent sees it coming.

Painful Memories: Doesn’t do much because the opponent will probably draw it. I like Lost Hours a lot more.
Dread Fugue: The comprehension complexity isn’t worth it for me.
Cabal Therapy: I haven’t tried this, but it might be too swingy by being able to nab multiple Death’s Shadows

Infernal Contract: This is insanely powerful
Foreboding Fruit / Blood Pact / Read the Bones: I haven’t tried any of these, but they could be worth it to downgrade Sign in Blood which is pretty powerful.
Vampiric Tutor: I don’t like how much time it takes to resolve this card, particularly if someone wants to try to deduce their opponent’s hand (similar to Mystical Tutor in Dandan).

Reanimate: This can get countered by Noxious Revival, Consecrate // Consume, and Orzhov Charm, so it’s not worth it.
Unearth: Sort of a Death's Shadow with cycling and the same downsides as Reanimate. I think Death’s Shadow is generally good enough that you wouldn’t cycle this, but I could be wrong.
Call of the Death-Dweller: This is only a late game card and I dislike keyword counters.
Profane Command: You don’t generally get that much mana so this is clunky. I also don’t like how the Fear mode does nothing.
Cremate: This didn’t have a big enough effect on games.
Misinformation: It’s pretty difficult to guarantee who will get which card because there’s many instant speed draw effects, so this isn’t worth the card.
Grim Discovery: This card didn’t excite me, but now that a Death’s Shadow starts in the graveyard, it may be worth testing again.

Devour Flesh: Too powerful as a one-sided sweeper.
Infernal Grasp: I think the main reason I cut this was because it was too similar to Dismember, but it could return.
Geth's Verdict: I think this was a little underpowered, but I don’t remember
Doomfall: Too expensive, but would be fun at 2 mana.

Apostle's Blessing: This ended up being too situational, either winning a game out of nowhere or doing nothing all game. Surge of Salvation fills some of the same roles in addition to countering discard spells.
Faith's Shield: This probably plays similarly to Apostle's Blessing, but I haven’t tested it.
Courageous Resolve: I haven’t tried this, but it’s probably too expensive, complicated, and not fun.

Most of the ETB tapped lands are just too slow and compete with the current ETB tapped lands.
Cabal Pit / Ifnir Deadlands: The activated abilities were almost never relevant while Tomb of Urami actually happens and is awesome.
Piranha Marsh: You’d generally target yourself, which makes this less versatile than Godless Shrine.
Mortuary Mire: This is too hard to set up for you to draw the creature, and you usually don’t want to give the opponent a Death’s Shadow.
Castle Locthwain: This was too powerful as both a card advantage engine and a way to quickly lose a lot of life.
Ebon Stronghold: I don’t remember testing it, but I’d guess the ability isn’t worth coming into play tapped.
Swamp: Not that exciting and makes Hagra Mauling more complicated and worse.

All of the following could fit, but none have been compelling enough to add dice or non-Death's Shadow permanents: Invasion of Gobakhan, Tangle Wire, Kaya, Ghost Assassin, Onyx Goblet, Braids's Frightful Return.

Misinformation feels cute, but often feels bad in hand.

Infernal Contract is really powerful

Trying out Imp's Mischief

Adding Scry lands and replacing some tapped lands. I may want to reduce the total number of tapped lands in the future

Speeding up the mana base

-Grim Discovery is too much of a late game card
-Painful Memories, I like that this never wiffs, but it usually does less than Lost Hours
-Devour Flesh is too good
-Blighted Fen, there's too much color requirements to play a colorless land

More speculative changes

Adding more variety to the lands

Initial cuts of cards I think are bad

Cutting the cube in half before I make further modifications