Viscera Seer is a repeatable sac outlet that can be used at instant speed and doesn't require tapping, meaning we can use it to trigger Sefris's venture ability on opponents' turns.
Carrion Feeder is a second copy of Viscera Seer, but more importantly, it is a Zombie, meaning we can re-cast Gravecrawler from our graveyard and have a repeatable sac fodder to trigger Sefris's venture reliably.
Gravecrawler is mainly in here to combo with Carrion Feeder and be able to consistently return and be sacrificed for Sefris's sake. Yes, it's one of only four zombies in the deck which makes its inclusion feel a little strange, however consider just how many graveyard tutors we have (i.e. Buried Alive, Oriq Loremage, etc). With these, we can consistently put together Gravecrawler with Carrion Feeder to reliably sac and recur Gravecrawler on each of our turns to venture with Sefris and save our instant-speed discard/looting to venture on our opponents' turns.
Bloodghast alongside a repeatable sac outlet is another great way to trigger Sefris. If we have a fetch land such as Prismatic Vista, we can play the Vista, revive Bloodghast and sac it to a Carrion Feeder and get a venture trigger from Sefris of the Hidden Ways. But we don't crack the Prismatic Vista until the next person's turn begins because when we do, the Bloodghast comes back and we can sac it again to get another Sefris venture. We'd be missing out on this if we played and cracked the fetch land in the same turn.
Reassembling Skeleton has a built-in reanimation ability, making it an excellent repeatable sac fodder.
Cathar Commando serves double duty as Artifact/Enchantment removal but also as a way to trigger Sefris's Venture ability. Since it sacrifices itself to activate its effect, it's perfect in this deck. Removal alongside a Sefris trigger and the nice thing is that if we have nothing better to reanimate once we complete a dungeon, we can bring back Cathar Commando and threaten more removal.
Ghostly Pilferer is fantastic in this deck because it gives us the option to draw a card if we have the mana to spare AND whenever an opponent casts a spell from anywhere other than their hand. This includes casting their commander out of the command zone. Finally, it's an instant-speed discard outlet so we can easily trigger Sefris of the Hidden Ways' venture ability on an opponent's turn.
Yuan-Ti Malison is unblockable as long as it's attacking alone, allowing it to get in for easy combat damage. And whenever it does deal combat damage to a player, we get to venture into the dungeon. This is one of many additional venture effects we have in the deck because if we're relying on Sefris alone to complete dungeons, the deck feels slower.
Triumphant Adventurer is sort of like a Glissa, the Traitor in combat as long as it's our turn. Whenever we swing with him, we get to venture into the dungeon and he's usually pretty safe to swing with thanks to First Strike and Deathtouch, killing whatever decides to block him before it can strike back.
Merfolk Looter can tap itself to let us draw a card and discard a card. The nice thing is that we can do this on opponents' turns, so if we've already triggered Sefris on our turn, we can save the Looter's tap ability to get another Sefris trigger on somebody else's turn.
Thought Courier is just another copy of Merfolk Looter and is in here for exactly the same reasons.
Selhoff Entomber is another decent looter except it requires us to discard a creature card first, so it's sort of an inverse looter but for 2 mana and considering we're playing 39 creatures in the main deck, it's not bad for what we want to do.
Vohar, Vodalian Desecrator is just another 2-mana creature with a tap-to-loot ability. It does give us the option to cast an instant or sorcery from our graveyard if we need it, useful for re-using a removal spell like Void Rend.
Obsessive Stitcher also has a looting effect so it serves the same purpose as Merfolk Looter. However this card also has an activated ability that lets us sacrifice it to reanimate another creature in our graveyard, just a nice option to have in a deck built around dumping cards in the graveyard.
Glasspool Mimic
is in here because it can copy one of our creatures for extra utility. Having two Radiant Solars for example means two venture triggers each time a creature ETBs on our field. It also enables a combo line with Cavalier of Night (see the Combos section for details). Worst-case scenario, we can just play it as a land if we need a land drop so it's never really a dead card.
Fleshbag Marauder, Merciless Executioner, Demon's Disciple and Plaguecrafter are all in here for the same reason - they guarantee a creature on our field gets put into the graveyard (they can sac themselves upon ETB) which gives us a Sefris venture trigger, and they make sure our opponents have to sacrifice one on their side of the board as well.
Nadaar, Selfless Paladin lets us venture when he enters the battlefield and whenever he attacks. If we've completed a dungeon, he gives our whole team a +1/+1 buff.
White Plume Adventurer lets us take the Initiative when we play it, meaning we get to venture further into the dungeon we're already in or we get to start Undercity which is by no means a bad dungeon to do. White Plume Adventurer lets us untap a creature on each opponent's turn, so we can do some extra looting with things like Merfolk Looter. If we've completed a dungeon, however, then we get to untap ALL of our creatures, giving them pseudo-vigilance which is great value. Furthermore, this will help us keep the initative with blockers meaning we'll get to venture on our upkeep as long as we have the initiative.
Yahenni, Undying Partisan is just a very reliable instant-speed free sac outlet because he can make himself Indestructible while triggering Sefris's venture ability on an opponent's turn. A great card to have in any aristocrats deck.
Seasoned Dungeoneer lets us take the initiative when it ETBs, which means an immediate venture into the next room (if we're already in a dungeon) or a fresh start on the Undercity. If we lose the initiative, Seasoned Dungeoneer makes it easy to get back thanks to its ability to grant protection to a Cleric, Rogue, Warrior or Wizard. If nothing else, it can grant protection to itself due to being a Warrior or our commander Sefris of the Hidden Ways due to her being a Wizard. Finally, the creature granted protection this way also gets to Explore, which means looking at the top card of our deck and essentially drawing it if it's a land or putting back on top or dumping it otherwise. This is a great way to get a free draw or dump a card to venture with Sefris for the turn.
Oriq Loremage lets us tap to Entomb a creature from our deck into the graveyard. Since this is an instant-speed ability, we can save it for one of our opponents' turns to make sure we're being efficient about our Sefris venture triggers.
Sakashima of a Thousand Faces lets us copy Sefris of the Hidden Ways and since it lets us ignore the Legend Rule, we essentially have two copies of Sefris on the field. So whenever we send a creature to our graveyard, we get a venture trigger from each of them. This is one way to bypass the usual "this ability triggers only once each turn" restriction. Alternatively, we can copy something like Elesh Norn, Grand Cenobite which means all of our opponents' creatures will have -4/-4, so everything with 4 or less toughness will just die immediately to a state-based effect if our opponents try to play them. These clones are very versatile in this deck and can chill in the graveyard ready to be reanimated once we have something worth copying.
Sakashima the Impostor is in here for the same reason, we can make another functional copy of Sefris except this one retains the name "Sakashima the Impostor" so we don't have to sacrifice either of them to the Legend Rule.
Spark Double is another clone that can get around the legendary rule by literally making itself non-legendary.
Corpse Connoisseur lets us Entomb a creature when it enters the battlefield. The nice thing is that it also has Unearth, meaning we can revive it from the graveyard without needing any other card to do so, so we can get value from it even if it was milled, killed or sacrificed earlier in the game.
Doom Whisperer has Surveil 2 at the cost of 2 life. Since this is at Instant speed and costs no mana, we can essentially do it whenever we want, allowing for easy Sefris venture triggers on our opponents turns. To Surveil, we look at the top 2 cards of our deck and can dump any of them. Roughly 1 out of every 3 cards in the deck is a creature so while it isn't guaranteed that we'll see one, it's fairly likely. Aside from all of that, it's just a solid 6/6 Flyer with Trample.
Abdel Adrian, Gorion's Ward is mainly in here because it combos with Animate Dead and Sefris of the Hidden Ways for infinite ventures into the dungeon. Since he's a creature, he can just chill in the graveyard and wait to be reanimated by Animate Dead, which we can be searched by Razaketh, the Foulblooded and retrieved by Cavalier of Dawn if it ends up in the graveyard so we have some combo resiliency and consistency.
Karmic Guide reanimates a creature when it ETB's and thanks to Echo, it then gets sacrificed on our next turn if we don't pay the cost, which is an easy way to get a Sefris venture trigger.
Mulldrifter can be Evoked to draw us 2 cards and then be sacrificed immediately after. Card draw and Sefris venture trigger all in one.
Reveillark can reanimate two of our creatures with power 2 or less when it leaves the field, which we can force by Evoking it. Crucially, however, it enables an infinite ETB/LTB loop with Kamic Guide and a sac outlet such as Carrion Feeder. Combine this with Radiant Solar on the field and we have infinite venture into the dungeon triggers. So Reveillark provides utility in a reanimator deck and enables some optional combo lines if we happen to assemble the right cards. Win-win.
Cavalier of Dawn is literally in here just to retrieve Animate Dead in case it gets blind milled by Altar of Dementia (of if it just gets removed or countered when we play it). Animate Dead is a crucial combo piece and we need a way to retrieve it in case it ends up in the graveyard. Cavalier of Dawn is a creature which means we always have an avenue to reanimate it with Sefris, then kill it with one of our sac outlets to retrieve any artifact/enchantment we need from our graveyard.
Cavalier of Night is amazing in this deck because of a multitude of reasons. First off, when it ETBs it gives us the option to sac one of our creatures and in exchange we get to kill an opponents. That is a venture trigger with Sefris on board and removal all in one. Next up, when it dies, we get to reanimate any creature with CMC 3 or less, so it's recursion as well. It does everything we want in this deck and opens up a combo line with Glasspool Mimic
and Altar of Dementia. See the Combos section for more details.
Radiant Solar is great value in this deck because it lets us venture into the dungeon whenever another non-token creature ETB's under our control. We're constantly reanimating stuff, so this will be triggering a lot. We also have the option to discard it and venture, which also gives us an additional venture from Sefris.
Elesh Norn, Grand Cenobite is just a fun reanimation target because it buffs our creatures, making them harder to kill while severely crippling our opponents'. If we copy Elesh Norn with something like Spark Double, our opponents' creatures with 4 or less toughness simply cannot exist on the board.
Toxrill, the Corrosive constantly weakens our opponents' creatures by debuffing them with slime counters on EACH end step, not just ours. Whenever one of those creatures dies, we get a 1/1 Slug token, which we can use as sac fodder for various effects in our deck or Toxrill's own ability, allowing us to draw a card at instant speed.
Avacyn, Angel of Hope is just one of the best reanimation targets you can find in white. Making all of our permanents indestructible makes them incredibly difficult to remove.
Razaketh, the Foulblooded does everything we want in this deck. It's a repeatable sac outlet at instant speed that doesn't require mana or tapping, meaning it's a great way to put creatures in the graveyard to trigger Sefris, all while being a Demonic Tutor effect every time we do so.