By a wide margin, my favorite cards in Vintage are the fringe playables. Those final techy slots in your deck can really give it a lot of personality, and perhaps even make it feel more like "your own." In most CCGs/Magic formats, the borderline usable cards almost always have a strictly superior version available. You wouldn't play a removal spell that costs three when you can get the same effect for two mana. Similarly, you wouldn't splash a third color for an effect you need if you can already get a similar effect from an on color card - and so on, and so forth. The cool thing about Vintage is that you get to choose from every card ever printed, which gives you access to a fair amount of unique effects that "have a reason to exist." In most cases, the cards in this list have a directly comparable cousin that sees much more play (example: Echoing Truth vs. Hurkyl's Recall). A few things on this list aren't like that (example: Blood Moon) - I just felt like including some strong cards that have been historically viable in Vintage and currently do not get played that often.
Viashino HereticAn amazing preemptive answer that can shut down Workshop decks all by himself. Only requiring one colored mana is extremely relevant, and he helps diversify your artifact hate while ignoring Thorn. He's also not a bad option against slower blue decks, as he can protect against Vault/Key or threaten to burn them out if they were to Tinker for BSC.
Comparable to: Trygon Predator
Potential uses: Blue control
Negate1U counters are not in high demand right now, but I wouldn't mind running a single Negate in certain decks. Snapcaster needs 1UUU to flash a Drain, and paying 2UU for a flashed Negate feels a lot more manageable. If your deck's goal was to set up a counter net on turn 1 with Mox/blue land, Mana Leak might be the better card for a catch all counter.
Comparable to: Mana Leak, Mana Drain
Potential uses: 4 color Snapcaster, Tezz decks
Dead/GoneThis is an intriguing card. For R, it removes Confidant, Welder, Lotus Cobra, etc. just as efficiently as Lightning Bolt does. You give up the ability to kill Jace and Lodestone in exchange for the extra out against BSC. It's nice to have a card that is good against random Aggro or Magus of the Moon decks while still having a usable effect against blue.
Lightning Bolt: Kills most relevant creatures, as well as Lodestone and Jace. Can be hit by Misstep.
Fire Ice: Kills most relevant creatures and can kill two x/1, but cannot hit Lodestone and Jace. Buys a turn against BSC, and can be cycled for 1U. Pitches to FOW. Cannot be hit by Misstep.
Dead/Gone: Kills most relevant creatures, but cannot hit Lodestone and Jace. Cannot be hit by Misstep. Cannot be REBed, unlike most other anti-Tinker bounce spells.
Comparable to: Lightning Bolt, Fire/Ice, Echoing Truth
Potential uses: Snapcaster decks, metagames with lots of Aggro
Spell SnareThere's some discussion about Spell Snare
here. We currently have an embarrassment of riches when deciding which counters to use. After FOW, you have anywhere from five to eight slots left to spend on some combination of Mindbreak Trap, Mana Drain, Mental Misstep, Flusterstorm, Spell Pierce, and Spell Snare. It gets even more complicated if you are running Duress effects that compete for space. Spell Snare is very metagame dependent, but still seems underused.
Comparable to: Mental Misstep, Spell Pierce, Flusterstorm
Potential uses: Any blue deck
Wipe AwayFor one extra mana, your BSC answer becomes uncounterable. This is potentially relevant with the rise of Flusterstorm...
Comparable to: Hurkyl's Recall, Echoing Truth
Potential uses: All blue decks
Vexing ShusherSpeaking of uncounterable, there may be a control deck out there that wants Shusher. He is included in RG beatz from time to time, but it wouldn't be crazy for him to show up in the sideboard of a heavy control deck in the future.
Comparable to: REBs/Flusterstorm, in that it helps you win counter wars post-board
Potential uses: a Keeper style deck
Echoing TruthThis sees a fair amount of play already, especially in an archetype like Landstill that doesn't dip into Green for more removal options. It answers BSC just as well as Hurkyl's Recall, while also getting rid of Marit Lage, Empty the Warren Tokens, or an Oath creature. The added utility of bouncing your own stuff can come up from time to time as well.
Comparable to: Hurky's Recall, removal spells like Fire/Ice etc.
Potential uses: All blue decks
Night's WhisperThis has seen tons of use in the past, and it still has shown up in a few brews lately. It will probably always play second fiddle to Bob going forward due to Bob's added resiliency against Workshops, but Night's Whisper is superior to Bob in many other instances.
Comparable to: Dark Confidant
Potential uses: A deck that already uses Bob
DeglamerThis was seen in T8's regularly when Demars Control was more heavily played, and I still like it a lot. Nature's Claim is better in most situations, but the added cost of 1 mana allows you to answer BSC.
Comparable to: Nature's Claim, Hurkyl's Recall, Ancient Grudge
Potential uses: Any blue control
Surgical ExtractionSince the release of Snapcaster, there has been an increased use of Surgical Extraction in sideboards. It probably should have seen play before that, and it's time to start considering Surgical Extraction as a maindeck card. Hitting Gush or FOW is pretty devastating and usually extremely unexpected. Even in matchups where a juicy target never presents itself, it still has lots of other functions such as countering Mystical/Vampiric, snatching a key card when Yawgmoth's Will is going to resolve, and so on. A singleton copy doesn't add much against Dredge G1, but it's worth mentioning.
Comparable to: Extirpate
Potential uses: Snapcaster decks, Grow decks, decks with discard effects or ways to see the opponent's hand
Hide/SeekAny kind of hate bear/beatz/aggro deck always hates to see Tinker. Even after a bunch of disruption, a topdecked tutor or Tinker can swiftly end the game while you were waiting to finish them off with a bunch of 2 power creatures. Hide/Seek is unique in that it deals with Tinker both before and after it is cast. Ideally you would snatch BSC out of their deck before they ever get a chance to play it, but being able to remove it from play is nice too. One key issue for Hate decks is usually the decision to run Null Rod or Chalice. Chalice is cited as the better anti-Tinker card, but pre-emptive removal cards like Hide/Seek may be a better answer. The strange color requirements relegate this card to a very specific BWR hate deck, but it still has some untapped potential.
Comparable to: STP, Sadistic Sacrament
Potential uses: Hate/Aggro
HoodwinkIt's like a bad Echoing Truth with some very rare/specific versatility added by being able to bounce a land. I can see some two color decks making use of it though.
Comparable to: Echoing Truth
Potential uses: Landstill
Noxious RevivalThis has seen moderate use in a particular build of European Gush decks, but I think it has a lot of untapped potential. If you're using it as a Regrowth, it's rare for the free mana cost to make up for the card disadvantage. However, the added versatility of being able to Time Walk an opponent in the late game makes this card extremely worthwhile. It also becomes a pseudo victory condition when combined with Snapcaster...
Comparable to: Regrowth
Potential uses: Almost any blue deck
Vendilion CliqueThis card is well known and sees a lot of Vintage play. Many people would consider it to be a Vintage staple. Even taking all that into account, it is still extremely underutilized. Neutralizing Jace, acting as a backup victory condition, acting as a backup counter spell, ghetto spot removal of Bob, gathering info about their hand...Clique is extremely versatile.
Comparable to: ???
Potential uses: Everything
Blood MoonThis doesn't have many analgous cards, since I think it has big potential in archetypes that would never consider Magus of the Moon. If you just click on a random top 8, it's astounding how many decks would have 0 outs against a resolved Blood Moon.
Potential uses: Aggro board, Red MUD, some kind of Standstill deck
What are some of your favorite fringe cards? Which of these cards do you feel is best positioned currently, and which have the most potential going forward? I really think Spell Snare will be seen a lot in the future if the Snapcaster/Bob Jace control deck continues to rise...plus it's quite good against the increasingly pervasive Landstill.