Solved games can be easily predicted and beaten if you memorize the sequence needed. We are fortunate that Magic and Commander are far from solved games. However, we are moving towards solving what is in an opponent's decklist. If you play a G/B Aristocrats list in Standard, your opponent will know what to expect. You have a sideboard and matchup percentages to throw your opponent off. In Commander, we have no sideboard luxury. If you play something well known, like a Krenko, Mob Boss or a Bruna, Light of Alabaster, most of your opponents will have a good idea of your deck.
How do you get an edge? Delve into less-known cards and off the beaten path for deckbuilding. We must find the diamonds in the rough, the hidden gems for Commander. The following list is not exhaustive by any means, but I'm presenting these cards to encourage you to delve into other cards outside the normal deck building set up. Sensei's Divining Top may be an extremely useful card for many decks, but it is by no means a must-have card.
Spirit Bonds is a card that got plenty of interest when Magic 2015 came out. It was a good Limited card but never really broke through in Constructed. Commander decks picked it up for the ability to generate tokens and protect key creatures, but over time I've seen less and less of this card as people forget about it or use other cards instead.
I particularly like the card in my Vish Kal, the Blood Arbiter deck, where all my creatures essentially have "Kicker W: Get a 1/1 flyer." Bonus points for saving my commander. Outside that, this enables neat Spirit sacrificing, like Yosei, the Morning Star or Keiga, the Tide Star. It also does great with Bloodghast and other creatures that return themselves.
Wing Shards saw a lot of play during the Onslaught era and now is mostly unknown. Do you know how many people cast a card before they attack, even when they don't have to? Most of us. Punish a player for dropping a mana rock and a utility creature before attacking; now they lose three attackers. Even better, the storm trigger means that the card can't be stopped by most counterspells. Your opponent needs Flusterstorm or something that can counter multiple spells.
Echoing Truth is super handy. Does someone have a scary thing? Bounced! Does anyone else have that same scary thing? Now they don't. For only two mana, the returns on this card are absurd. Love Declaration in Stone? Try its pseudo-predecessor. Bonus point for hitting tokens after a Secure the Wastes or an Avenger of Zendikar to slow someone down for a single instant.
Oona's Grace draws a card at instant speed and can be recast for only three mana every time you start flooding. Oona's Grace is even better with stuff to get lands back or play them from the graveyard. This card isn't splashy, but a small workhorse that does a little all the time and won't be stopped is often a lot more solid for decks than a card that peacocks and challenges the whole table to bring you down. This card is a favorite of mine in Jori En, Ruin Diver to trigger both her card drawing effect and to draw an extra card off the spell itself.
Muddle the Mixture stops a whole boatload of bad stuff. Your opponent casts Genesis Wave for roughly a trillion? Nope. Although it cannot halt an opponent's creature, the counter ability combined with a tutor effect is wonderful. Need to find a combo piece, a bit of removal, a utility creature, or a powerful enchantment? Go get it! When things get desperate, you can even tutor for a different tutor spell like Demonic Tutor or Open the Armory to find what you really need. Sometimes it's the early game and you are struggle to make land drops, Muddle the Mixture will help the cause and go find a mana rock or Rampant Growth.
Thada Adel, Acquisitor should definitely see more play, maybe as a commander or maybe just as part of the 99. Either way, she needs more love. Early on, you can steal Sol Rings and Thought Vessels from opponents to boost your mana into the stratosphere. Nearly every table has an opponent or two with an Island. Later on, you can snag Soul of Phyrexia, Steel Hellkite, Duplicant, or even a Mindslaver to stop an opponent from locking down a table or player. And feel free to cue up All the Single Ladies on your phone for the first Sol Ring you snag (Rings of Brighthearth will do in a pinch).
Elbrus, the Binding Blade is a fantastic card for flavor; the Demon bound in a blade is unleashed. This card does take a little bit of work to cheat out, or just eight mana. Withengar Unbound is a massive 13/13 with three types of evasion. This Demon can only be blocked by a flying black or artifact creature, and even when Withengar is blocked, he tramples right over the blocker. Getting thirteen counters on him after someone loses the game can close out games much more swiftly than most opponents can react. Even foil copies are only $9.99, if that matters to you (it looks sweet in foil).
Grim Harvest is frequently left behind in deckbuilding. With Coldsnap being out of print for a decade, this Raise Dead variant is buried in boxes of commons. I highly recommend you go find it. Grim Harvest is an instant, and recover lets you bring it back when a creature dies. The Lorwyn Elementals with evoke make this card spectacular. Need a ton of cards in hand? Add Mulldrifter. Need to stop flying tokens? Add Cloudthresher. Need to stop graveyard shenanigans? Add Offalsnout. Even without evoke, the recover mechanic helps you get back in the game after a battlefield wipe.
Shred Memory does work! This card works similarly to Muddle the Mixture where it has an actual in-game effect and can tutor for a useful two-mana card. Exiling cards from the graveyard at instant speed is definitely underrated by Commander players. Don't be one of them! Use good cards with real effects for being cast or transmuted.
Ink-Eyes, Servant of Oni is a card that once saw lots of play and now is relegated mostly to the forgotten bulk piles. As a commander, Ink-Eyes cannot use ninjutsu to cheat onto the battlefield, but she can as part of the 99. Either way, regenerate is pretty handy with Supreme Verdict, Day of Judgment, In Garruk's Waste, Pernicious Deeds, and loads of sweepers without the “cannot be regenerated” clause. The best part of Ink-Eyes is that she steals creatures from your opponents. Even something as simple as a Solemn Simulacrum or a Sakura-Tribe Elder generates value. Stealing something extra-spicy can completely wreck the game for your opponents. Give Ink-Eyes, Servant of Oni a try and see what a Rat Ninja can do for you.
Dwarven Blastminer actually represents a few cards: itself, Dwarven Miner, and Trench Wurm. All three present ways to remove problem cards from an opponent, like Maze of Ith; Urborg, Tomb of Yawgmoth; Gaea's Cradle; Eye of Ugin; or whatever problem land is showing up. If you want, you can go after people's manabases too. But I like the cheap, repeatable ability to remove lands that only cause issues.
Viashino Heretic is a wonderful tool against artifact decks. It either kills an artifact or you get to live the dream and target something like Darksteel Colossus so you can repeatedly hit them for eleven. Even without getting a ticket to Magical Christmas Land, destroying Gilded Lotus and dealing five, Staff of Nin and dealing six, or destroying a Sword of Feast and Famine and dealing three damage with an old uncommon is serious power.
Flame Jab is not going to win any awards for power or style. But Flame Jab does turn late-game draw spells into Blaze. If you cast Blue Sun's Zenith for a whole bunch and draw lands, Flame Jab has your back to whittle away at utility creatures and players alike. Flame Jab is also pretty handy when you need to finish off a planeswalker or some big creature that already took some damage.
Subterranean Spirit's effects wreck tokens. Did an opponent make infinite squirrels with Earthcraft and Squirrel Nest? They're all gone. The card even has protection from red so you don't need to worry about Pyrohemia or Earthquake taking away your Elemental Spirit. Oh, and unlike Goblin Sharpshooter, this can rumble into combat without embarrassment.
Frostwielder is a hidden gem because she exiles. She doesn't need to deal the killing blow; she just needs to contribute and that creature is exiled. Wurmcoil Engine, the Champions of Kamigawa Dragon cycle, basically anything with a dies trigger…she shuts them down. Watching players waste a Swords to Plowshares or a Path to Exile to remove her as a threat is a wonderful feeling. You haven't lived to the fullest in Commander until you cast her and shut down a deck.
Parallel Evolution is a huge play for token decks. Double everyone's tokens. Pick your path to victory using tokens and go for it, whether it's haste and pump, or Zulaport Cutthroat and a sacrifice outlet, or Purphoros, or something else. It doesn't matter! You just doubled your tokens. Even better, the card has flashback so you can do it all again. Everyone knows about Doubling Season and Parallel Lives. Parallel Evolution is the original Second Harvest; give it some well-deserved love and watch it blow out your opponents.
Hurricane and its sibling Squall Line are way underloved in this format. Sometimes a green deck can't break through, or there are so many flying creatures that you can't see the sky. Hurricane gets rid of that problem with direct damage to everyone and all flyers. Unlike Earthquake and Fault Line, where a red deck has to wipe its battlefield to plow through opponents, green decks typically lack fliers, so Hurricane leaves your battlefield intact and takes care of any potential blockers. With the Spirits in Innistrad starting to show up more and more in Commander, these cards are getting better.
Deglamer saves games. Do you know what is infuriating in Magic? Not being able to interact at all. The Theros Gods are nearly untouchable for many decks. Exile or sacrifice them; that is it. Oh, they can be bounced, but they are aggressively costed and come right back. Deglamer either tucks a God into the deck or shoves a God back into the command zone. For regular enchantments, Deglamer just shuffles them away. Unravel the Aether is just as good; in fact, you should probably run both.
Become Immense kills people. It is my favorite card in my Silvos, Rogue Elemental deck. Smack someone once, attack again. If they gamble that they can get to sixteen commander damage, you slam Become Immense and wreck face! Even in decks without an eight-power commander this card is good. Lots of the most efficient pump spells can be great in Commander; but we are often told that they do too little. Vines of Vastwood, Krosan Invocation, and Might of Oaks are also great in Commander. Rumbling into the red zone is fun; rumbling with better creatures is even better. Be even better and play your pumps.
Spore Frog, because Spore Frog. Fog Frog saves you! It triggers Meren of Clan Nel Toth like a boss and can be recurred in lots of different ways in white, black, and green. Nim Deathmantle turns Spore Frog into a four-mana repeatable Fog. Give this little Frog a try.
Crystal Ball may be “objectively” worse than Sensei's Divining Top, but it has uses. For a budget, it is a huge difference. But the real strength of Crystal Ball is that you don't need fetchlands to move past clumps. Activating Top and seeing triple lands is kind of miserable. Scrying two lands to the bottom of the deck is really handy for drawing into gas.
Tarnished Citadel is an often-forgotten card because it was often terrible. But 40 life and the colorless Eldrazi cards make this better. It gives colorless most of the time, but when you really need a color, the Tarnished Citadel is there to help you out. I have a “totally a commander” Dune-Brood Nephilim deck that loves this card. Most times it's just helping out, but when I really need a fourth color, boom! I take a Lightning Bolt and fix my mana all at once. If you're struggling with colors, maybe you should try this.
Blade of the Bloodchief pumps creatures a lot, most often a commander. Lots of things die and this card is too overlooked. If a deck uses +1/+1 counters or the commander uses them, this card is definitely worth a second look. VIsh Kal, Blood Arbiter; Deathbringer Thoctar; or Triskelavus with Blade of the Bloodchief is excellent. Your opponents will know to destroy a Sword of Fire and Ice, but how will they react to Blade of the Bloodchief? Play it and find out. Then get ready for the fun.
Loxodon Warhammer is a pet card of mine. Pump up a commander or a big fat creature, trample, and gain life. I'm not a fan of pure lifegain cards, but giving Oros, the Avenger or Bloodfire Colossus lifelink and activating either ability is extremely rewarding. This hammer can go into any deck and turn any creature into the mighty Thor. Here's a tip: this card costs six mana. You may cast it for three and then wait to equip it, but it is a great way to lose the card. Pretend it costs six mana and you will be much happier with your Elephant hammers.
What hidden gems do you have? Any card that most players need to pick up and run? Some of these cards may not be the most efficient, but a less efficient card that advances your gameplan is often better than a more efficient card that does nothing to help the deck. Find some hidden gems to break open games with your group!