Since you're playing the Ghost Quarter/Arbiter package, Mana Tithe can be a literal counterspell in the late game as well as a "gotcha" spell early on. One Crucible of Worlds would be a great addition to keep the mana denial going in the late game. Also, I think you need to go up to 5 or 6 discard spells, like a 3/2 split of Thoughtseize and Inquisition of Kozilek or something. 4 Thoughtseize seems a little sketchy to me. Maybe a little bit of card draw to find Maralen more easily could be okay, like Sign in Blood. You won't draw it after you drop Maralen (obviously) so it's not really a nonbo and if it's in your hand when you play her you can just point it at your opponent for 2 dmg.

Have you considered playing the Phyrexian Unlife/Solemnity package rather than Madcap/Emperion? The good points are that it's 3 mana rather than 4 and Enchantments are harder to remove than creatures are, the downsides are that it's a 2-card combo rather than 1 card (although Phyrexian Unlife on its own prevents you from dying to Maralen and Bitterblossom so I suppose you don't necessarily need Solemnity in that sense) and it's riskier because you can lose if you're at 0 and they manage to kill the Unlife through the land destruction and Mana Tithe (put it in pls), which isn't a problem with Emperion. I'm pretty sure mtggoldfish showcased a similar Maralen deck on an instant deck tech a while ago, except it was BW. I don't remember exactly but I think there were some sweet card choices that could find a home in your deck.

Thanks for the feedback hungry000. I've playtested both the solemnity/unlife combo and this one. My conclusion is that the madcap is superior because being significantly faster as well as adding pressure to the board to close the game backs up the soft lock version of maralen better.

I'm also toying with the idea of keeping solemnity/unlife in the SB at 3 copies each and just switch them out in matchups where creature and artifact removal is expected game 2.

I've also tested more prison oriented Maralen in esper (silence and shadow of doubt with isochron scepter) and abzan colors (double down on the land hate with assassin's trophy) and in those kind on decks, that aim to get hard locks, the phyrexian + unlife combo is indeed superior.

I like your other suggestions and I'm going to try them out. I agree the hand disruption needs to be 5-6 but I figured Collective brutality acted as number 5 and 6 there. I personally think 4 thoughtseize is fine as we're not losing life from it in the lategame, but I might be wrong. Mana tithe is an interesting suggestion, sounds like it could be great sometimes but also really bad a lot of the time. I'm not sure if crucible of worth it but I'll try it out as I have a set.

Any suggestions what to cut, I'd rather not go down too much in consistency. Off the top of my head I can see cutting maybe 1 maralen for crucible and maybe 1 bitterblossom for sign in blood, but that slot could also go to dark confidant if card advantage is the goal since he keeps drawing under maralen.

I see. I don't usually count Brutality in the "discard spell" category since it's flexible and it isn't 1 mana. I'm not really against 4 Thoughtseize but I don't like being at a very low life total early on in a grindy deck, even with Emperion. It feels like there's not enough margin for error. I've played a Maralen deck once before, and Mana Tithe performed pretty well for me. I also made a Butcher of the Horde deck and just stuck it in because I like it, and it worked there too. I think Crucible is amazing in any grindy Arbiter/Ghost Quarter deck, especially this one since it can be searched out with Maralen. I tend to prefer the grindy lock type of gameplan if it's possible whenever I play midrange decks though, so I may be biased.

Maralen is pretty important so I believe it's best not to cut her. Bitterblossom looks like an ok cut, you could go down to 3 Aven Mindcensor as well since they're not good in multiples and not as good as Arbiter, maybe go down to 2-3 Bolt. If you're putting in card advantage going to 23 lands doesn't seem like a bad idea either.

The main problem I see with crucible is tempo.

So typically when the land destruction is relevant we're aiming to play Maralen on turn 3 or 4, either turn 3 after arbiter or turn 4 after mindcensor, if we're on the land disruption plan that means we've played arbiter first, so we have 3 or 4 lands and our opponent hopefully has 2 or 3. We spend 2 of our mana to search each turn and run through a couple of our ghost quarters to keep them locked, at that point our life total as well as theirs are below 10, we have a maximum of three searches left and those usually needs to go towards fetching madcap experiment and maybe a land to cast it, and if we don't need to do that it's because we're ahead in the race and our opponent will die first, and if the difference is minor a bolt to tip the tide is what we can cast with our free land on the same turn we're searching.

In short, I don't see a window to cast crucible in the typical Maralen lockdown scenario. My goal is to lock followed by pressure, if I can locke them 3-4 turns I should have won or established a winning lead, so when I'm land locking 4 GQs are plenty enough in most cases. The situation for my enemy I'm trying to establish in this version is not really "I can't play anything" and more "I don't have time to play for the win because I'm dying first if I do".

I feel like the way to break Maralen is to understand that she's not primarily a control piece or a lock piece in the first place, she's an aggressive clock and a value play to support with more pressure. If we get in 3-6 damage and a search of better quality than our opponent while nulling their draw spells and blanking their gameplan for 1-2 turns that's fine if she dies, it should be enough value for one card to establish a lead or close the game.

I've always been a fan of madcap since kaladesh's standard with gearhulks. Love the take on maralen, and the deck seems like alot of fun to play.

Finally, a new way to use Maralen! Great job. +1

Looks like a fun deck! Good card synergies in there. Not sure if it's legal in modern, but you might want to run Stranglehold in this deck. Even if you probably won't be able to get it on the field before Maralen (due to it's higher mana cost), the two together would absolutely shut down your opponents.

PenaltyBox thanks, Stranglehold is not modern legal unfortunatly, I think if it was legal Maralen Prison would have been a more established modern archetype by now.

More prison oriented Maralen decks use Mindlock Orb, but it requires the deck to be built around it and I don't think it's that good anyways.

An extremely intuitive deck! Another one of the coolest decks I've seen on here. Looks like a load of fun to play, especially with all those Maralen interactions I never knew about! +1

I think that Ob Nixilis, Unshackled would be a fun choice and could either end the game pretty soon after being played or just really force your opponent to not draw and also lose for not having anything to play.

Thanks for the suggestion EthanJones1 , I think Ob Nixilis is too slow for this deck at 6 cmc though, you can't really spend Maralen triggers on fetching a bunch of lands so I want the curve to top at 4.