The primary purpose of this deck is to get Dark Depths into play as early as possible, and then use some means of cheating the entrapped, eldritch sorceress Marit Lage into play immediately after that.
The first thing is to ensure that you have Dark Depths available as early as possible. Realms Uncharted, Expedition Map, and Sylvan Scrying are definite four-of cards as cheap ways to find Dark Depths early. Realms Uncharted lets you tutor it out, along with a Thespian's Stage very early, and then you can use one of several different cards (more on that below!) to yank it out of your graveyard if that's where it ends up.
The next thing is that you need to do is get The Wiggly One who Sleeps Below the Ice on the field. 30 mana is a lot to pay, even for a creature that's basically a one-hit kill, so we aren't going to do that! Vampire Hexmage and Thespian's Stage provide easy (and cheap!) ways to remove all of the counters on a resolved Dark Depths and get Marit out much earlier than she should be.
But what happens if you do somehow lose Marit Lage? You need a way to get your win condition back as soon as possible!
The biggest challenge here is that you have to retrieve Dark Depths from the graveyard. Eternal Witness, Grim Discovery, Tilling Treefolk, and Life from the Loam all provide inexpensive ways of getting that all-important legendary land back into your hand. Tilling Treefolk and Life from the Loam also provide you with a neat way to get your Thespian's Stage back, too, if you sac'ed that to trigger Marit's ascension.
Harmonize is the final part of the deck, and sits at the very top of the mana curve. This helps you recover a few cards after you've spent and sacrificed a handful to your eldritch goddess, which prepares you to dredge more cards from your graveyard and get her out again as soon as you possibly can. Alternatively, if you end up with extra cards in hand at the end of your turn, dump the best ones in the graveyard, and use the aforementioned tricks to get them back at your leisure!
For the sideboard, I tried to consider what kinds of strategies that this deck might be weak against, and looked for a little bit of hate for each one. Ranger's Guile, a one-drop that makes a target creature hexproof until end of turn, is probably going to be your new best friend, as it protects against removal, bounce spells, and exiles altogether. Mental Misstep provides a little extra insurance against bounce spells. If your token does get bounced, you need to use the graveyard strategies above to get her back out again, which can cost valuable time. Oblivion Ring and other related exile enchantments are probably second only to bounce spells, so for that, you 'board in your Naturalize and destroy the offending enchantments. Finally, while Marit herself is immune to the popular Doom Blade, and Ranger's Guile will protect against Go for the Throat, you may still have to deal with removal spells that force you to sacrifice a creature. In this case, swap in your Tajuru Preservers and nip that nonsense right in the bud. Even if it only buys you a single turn while they spot-remove your Preserver, you only need to connect once -- one turn might just be enough.
That about covers it. Enjoy killing much more expensive decks with a hyper-powered, immortal sorceress from beyond the realms of god and man alike!
Ia! Ia! Marit Lage f'taghn!
