Found this expansion through the second installment of the series. Overall I love the flavor of the set and how the risk and reward Doom Clock mechanic works. I looked through the entire 135 card set since I was interested to see the full set and scope of the project (in terms of Constructed mode) and I believe the themes and playstyles blend very well across each class and the expansion as a whole. While I won't go into a full and thorough critique and card review, I at least wanted to cover some specific cases and cards that were "pain points" for me while I was soaking in this expansion.

Firstly covering two pain points of the main and major mechanic of the expansion, Doom Clock.

Currently the Keyword tooltip box reads, "Once you activate it, it counts turns towards your inevitable death. Keep resetting it or stop it to survive it."

A few things about this description look and feel too wordy or longwinded to make it seem like it would fit and exist in Hearthstone. Now I understand that Hearthstone has been reaching a point where the devs are beginning to try more unique and ambitious designs in the game. But look at Murder at Castle Nathria's keywords/designs just revealed. Infuse's description is incredibly concise, clear, and to the point. 

So in my view and opinion as a semi-experienced game dev (currently in college for game design and have worked on teams for multiple course's game projects), I believe the Doom Clock keyword should be condensed to this: "Counts down X number of turns. Upon reaching 0, your Hero is destroyed."

This version of the description is much more concise and clear how it operates. Since cards utilizing the keywords set, pause, or stop the Doom Clock themselves, the only information the actual keyword needs to provide is what is happening (the turn countdown) and what happens when the countdown reaches 0 (you die/lose). Any extra information is either unneeded or can be experienced and learned from in-game or via gameplay footage the devs create for marketing.

The second aspect of the Doom Clock keyword that stood out as a pain point to me is that any card that references setting the clock reads "Set your Doom Clock on X turns." The word usage of "on" here looks and feels very odd to me. Why doesn't the effect just read, "Set your Doom Clock to 3." This wording of the description keeps the completely same effect and even cuts off the word "turn" at the end which can (and should) make text formatting on more advanced cards easier and cleaner. And setting your Doom Clock to a number makes it easy and obvious to connect to the keyword because you can then hover over the card and see that the number being set is the "X" in the description.

Secondly, on to some specific cards that stood out to me.

Mal'Ganis the Inevitable: Unless you have been able to set up some form of card testing environment to feel out how Doom Clock plays out in fairly representative games, the Immune part of this card's effect seems far too strong and accessible to be balanced for the game. The Immune keyword in Hearthstone has always been either temporary or in some way interactable with. In the case of the currently existing Mal'Ganis in Hearthstone, he only provides your Hero Immune while he is alive on the board. If your opponent can kill him off, they can then start interacting with your Hero again. As it stands with this card's current design, if you get him down on the board with the Battlecry trigger, you'll have a permanent 9/7 on board for the rest of the game. NOTHING would be able to destroy or interact with it. I tried to come up with an alternative design or keyword to take the place of Immune but honestly it would change the card too much if you are trying to keep its design a callback to the old Mal'Ganis. This is also why I believe the Hearthstone devs themselves have not created a retrain of Mal'Ganis yet, because whatever they would design for a new version of him would have to be something completely new or different than what his existing version does and is themed around (Demons and Hero Immunity).

Doomer: I feel like the aura effect, "Your Doom Clock is paused." makes more sense than the current description, because the current description's word choice of "move" could be misconstrued as a physical action rather than temporal action, especially across card translations throughout the world. Pausing a clock makes more sense anyway, and the aura effect remains the same of preventing the Doom Clock's countdown from increasing or lowering. Also, a paused clock can be stopped (which the Bringer legendaries do) whereas it is unclear if an unmovable clock can or can't be stopped.

Future Memories: Currently this card's effect is incredibly confusing and unclear to the average player, as well as not accounting for / being worded correctly to make sense on both the player's turn and the opponent's turn. A more clear and understandable version of this effect, which retains the same outcome/goal of the card and can still be formatted well should read, "Secret: When your hero takes fatal damage, prevent it, become Immune, and restart that turn (Without this Secret)."

Doomsage Arkaan: Overall the majority of the Bringer legendaries' effects are worded in ways that are clear and understandable enough to make sense to the average player. However this card's effect is the exception and actually made me do a double take on it since the wording didn't make total sense to me when you described the card as super powerful/impactful. It made me realize that these Bringer legendaries would really benefit if they utilized the "(Upgrades when X.)" wording instead of a frontloaded effect. Here is my rewording of the effect that retains the same outcome/goal and makes it more clear and understandable: "Battlecry: Stop your Doom Clock. The next three spells you cast cost (1) less. (Upgrades each active Doom Clock turn.)".

Overall I hope my feedback and criticisms help and improve your custom card designs in the future. I firmly believe that you're a great card designer and would work greatly on the Hearthstone (or another card game) development team if that's your goal down the line. However I do believe that there is some wording and grammar aspects of card design that you need to work on and improve since there was a handful of other cards I didn't cover in this expansion set that had clarity or word choice issues. I'm not saying this to try to be rude or belittle you, it's just the only aspect of your card design that stands out to me as something that can be improved and learned from as you create more custom cards. Have a great rest of your day!