While each variant of Nic Fit gains access to its own sideboard options, there are several cards that are generally agreed upon as common sideboard cards across most archetypes.
Some of the better graveyard hate in the format. Naturally solid against pretty much any combo deck – especially considering we play discard spells. Surgical also gives us some game against reanimator and lands. Combo decks are generally our worst matchups, so shoring them up out of the sideboard is a priority. Surgical occasionally has other fringe uses – if someone Brainstorms in response to a therapy, Surgical-ing something lets you see their hand pre-therapy, and shuffle away anything that was hidden on top of their library. Usually it’s best to only do so if there is a relevant business card already in their graveyard to target with Surgical, though, and I wouldn’t bring Surgical in against non-combo Brainstorm decks. Surgical is also the best extraction effect that can target lands, so it’s helpful in that matchup – given the choice, take Thespian’s Stage, since Dark Depths is more useless than Stage is on its own.
LL is a very underrated combo hate spell. Unlike Slaughter Games, it costs three mana which is a big deal and makes it much easier to cast on turn two. Usually you want to take an opposing combo deck’s win conditions – Tendrils/Wish against Storm, and other namesake enablers like Show and Tell are also solid calls. Against Reanimator it’s helpful to know what they are missing, but Entomb, Griselbrand and Reanimate are all reasonable choices. Taking Natural Order or Craterhoof away from Elves also slows them down significantly – usually you want to take NO if they might be on Progenitus, and Hoof if you’re confident they aren’t. Also useful for taking Loam against Lands.
Like the above, good against any combo deck, though I wouldn’t bring it in against Lands unless I had nothing else. Thoughtseize is a pretty standard hate option and pretty much always does something useful. Some builds run it in the maindeck as supplemental discard in addition to Therapy, though Brutality competes a lot for that slot. If you do run it in the maindeck, make sure you have something available to swap it for against aggressive decks where your life total is under pressure.
To the Slaughter/Edict effects
SOI block saves the day once again. TTS fills the same slot as other ‘single target’ spot removal spells such as Vindicate, Maelstrom Pulse, and Anguished Unmaking. It has a few advantages over the others, though – it is one of the only available choices which can, at instant speed, get rid of any of TNN, Jace TMS and a Marit Lage. It’s also a solid 2-for-1 in some grindy matchups where you can get Delirium (though it isn’t necessary to be a good card) and has a relatively unrestrictive mana cost.
Diabolic Edict is another choice for an “edict” effect to deal with those pesky True-Name Nemesis’ (Nemesi?) and Marit Lage. Instant speed is the draw (similar to TTS) but costs one less mana and loses the ability to “get” a planeswalker. The argument for Diabolic Edict is moreso if you anticipate a field of Marit Lage. Being a turn faster is important as those decks generally will try to churn out a 20/20 sooner rather than later.
Pulse of Murasa
Good for anything which is going to be grindy, Pulse also doubles as Reanimator hate in a pinch (it doesn’t have to target your own graveyard). Pulse of Murasa also is very solid against people trying to burn you out, as the lifegain is not negligible. A lot of slow grindy matchups can quickly end off a couple DRS activations and a bolt-snap-bolt, and this helps a lot there. Six life is also often enough to put you over 20 even after fetching a couple of times, which means you can use it to survive a swing from Marit Lage and then deal with it at sorcery speed, which is a useful tool to have available.
Zenithable artifact/enchantment hate is a lovely thing to have in the toolbox. Like Witness, Sage also provides a cheap disposable body to fuel sacrifice effects with. If you want hate for this sort of thing then RSage is probably the go-to answer, simply because it gives you five effective maindeck copies via Zenith for only one sideboard slot, which is a lot of efficiency. Sage is a bit on the slow side, and you do already have access to Pernicious Deed and Abrupt Decay, so it’s not completely necessary, but it’s not often a card you will regret putting in your side.
If you’re running a reasonable number of small creatures (particularly Dryad Arbor), Jitte is a great answer to other small creature and aggressive decks. If you’re playing Stoneforge it’s probably in the main, naturally, but drawing it when you have any form of board presence probably demolishes a deck like Elves, D&T, or any Delver variant. It’s vulnerable to Kommand and doesn’t do much if you don’t have an established load of creatures on the board, but if you can get around those issues it’s one of the faster and cheaper ways to take control of the game and stabilizes pretty solidly.
Carpet of Flowers
Previously a mainstay of Nic Fit sideboards, Carpet is less popular now. Carpet helps a lot against mana denial out of blue decks – i.e. Delver – and also give you the option of siding out Explorers against decks you don’t want the triggers against, such as Miracles-style hard control decks. Currently, however, Miracles is a lot less popular, and a lot of other blue decks run Leovold. Leovold absolutely wrecks Carpet of Flowers, drawing your opponent two cards every turn for as long as Carpet is in play, and bringing it in against a BUG deck is now an extremely risky plan, so I wouldn’t recommend it currently.
Leyline of the Void
This thing is an absolute beating for a lot of decks right now, and we can reasonably cast it quite a lot of the time. It competes for Surgical Extraction’s slot, and usually loses out because of its weaker effect against less yard-dependent combo decks like Sneak and Show. However if you see a lot of graveyard dependent decks in your metagame Leyline is certainly a solid choice, or you have other synergies which work well with it.
Pithing Needle / Sorcerous Spyglass
A catchall answer to a lot of problem permanents. Has a lot of relevant against planeswalkers, Lands (especially Thespian’s Stage), Aether Vial, Equipment, Helm of Obedience, and Grindstone. Doesn’t like Deed very much, but against a lot of the deck you want this for you are cutting Deeds anyway. Spyglass is the option I would go for, since it’s a little friendlier with deed and occasionally you get to blow people out if they have two of the same fetchland in their hand or something, and it has synergy with Cabal Therapy. It’s also castable into a Chalice if you really need to turn off that Eldrazi player’s Jitte/Endbringer or Big Red’s Sneak Attacks.
Bridge is a solid include against Lands, Show and Tell, Reanimator and Elves, which is a relatively unique slice of the meta game for a hate card. It is vulnerable to most forms of removal those decks would sideboard in – but at the same time, all our other hate for those decks tends to be hand disruption or removal, so this a completely different angle of attack for us to use. It does also shut our own clocks down somewhat – however we don’t have to actually empty our hand for this to be good, it’s more about stopping Craterhoofs and Marit Lage than anything with less than 4 power. If our opponent does stonewall us with an Emrakul or whatever, we can usually get around it or find removal eventually – Bridge does buy us a ton of time even if it slows our clock down somewhat.
Generally speaking, most Nic Fit shells will have sweepers main-deck in the form of Pernicious Deed/Toxic Deluge; however, given the limited space in the maindeck, having additional sweepers are often backbreaking against creature-based decks.
Additional copies of Decay and Brutality can go in the sideboard to improve midrange/sfm and aggro/burn matchups respectively.
Metagame specific creatures
Scavenging Ooze and Deathrite Shaman are zenithable graveyard hate – if you don’t have either in your maindeck, you pretty much definitely want one of these in your sideboard unless you have a very good reason why.
Vraska Relic Seeker, Ob Nixilis Reignited, Garruk Relentless, Carnage Tyrant, Titania. If you want something to break open fair matchups, you have a lot of options. Primarily these choices need to be resistant to removal, end the game on their own given the opportunity, and also help to stabilize the board in some way. This sort of thing you usually don’t want in the maindeck (unless your meta is freakishly fair, in which case go right ahead) because it’s just too expensive against tempo and combo decks. Often fair midrange decks are already good matchups, so you don’t want to dedicate too many sideboard spaces to this sort of thing, but having a couple options to bring in when you take out any irrelevant cards can be nice for really hammering a matchup home. You will often have at least one or two haymakers maindeck but having additional options in the sideboard will allow you to swap one or two that may be more impactful in particular match-ups.
Emrakul, The Promised End
Emrakul is a special case in terms of haymakers. This guy is the be-all and end-all of winning control matchups. He is generally something along the lines of a 4-for-1, sometimes more, and honestly ends the game in almost all scenarios. The spaghetti monster is not to be underestimated. He’s also playable into other slow-ish fair decks, like most BUG builds and the mirror. He is not something you want to be running into anything unfair, or featuring Delvers, however. If you are running Emrakul in the sideboard, you usually want a Fierce Empath, to allow you to Green Sun’s Zenith for him. Note that he is quite difficult to cast. The most reliable route is to play a Primeval Titan, allowing you to Zenith for Empath, find Titan, fetch up Volrath’s Stronghold + Phyrexian Tower, and use them to recur Empath for an Emrakul, while Titan finds you the lands to cast him. It’s slow, but it doesn’t require you to dodge removal much, and if they deal with Emrakul you can keep recurring him with Stronghold and Tower until they lose (which is usually not a long time). Emrakul is slow, awkward, and probably overkill, but if you ever wanted to bring a freight train to a knife fight, this is where you find it.
Example Sideboard (excluding non-GB options):
3 Surgical Extraction
2 To The Slaughter/Diabolic Edict
2 Lost Legacy
2 Toxic Deluge
1 Sorcerous Spyglass
1 Reclamation Sage
1 Pulse of Murasa
1 Vraska, Relic Seeker