Iwamori of the Open Fist

Obviously this was more of a drawback in the Legends Matter block, but it’s much less risky now. A trampling 5/5 for 4 mana is pretty good, especially when they have some 1/1 tokens to chump your Blastoderm.

Jabari's Influence

Note that the creature needn’t have dealt you damage, just attack. Stealing is like removing a creature and playing one at the same time, and doing it on their turn means you'll be able to attack with it on your turn.

Kaervek's Purge

Just a solid (if expensive) piece of removal, with some nice burn tacked on. This card is like two fireballs in one.

Kaho, Minamo Historian

If they kill it, it’s still just a one-for-one. If they don’t, it’s huge. You tutored for three instant cards for 4 mana. And what if you make one of the removed cards an instant-speed protection spell like the cantrip Shelter?

Lashknife Barrier

It cantrips! Which makes up for the fact that this is very dependent on what creature cards you’re playing. You’d be hard pressed to find a better combo with Pestilence, though. 

Legacy's Allure

A Legacy semi-staple for a quarter. Any way you look at it it’s going to cost them a card, either some early enchantment kill or a creature. It may also cause them to put off playing creatures, which helps as well. 

Lethal Vapors

Skipping a turn is far harsher than the 4 damage of AEther Storm, but effects like this are only truly powerful if you’re able to take advantage of the situation.

Liar's Pendulum

A fun effect that should draw you a couple cards.

Mindblaze

This card was not intended for Singleton formats, but here it’s either a fun guessing game or a guaranteed 8 points. Do you have enough information by turn 6 to get into their head?

Mist of Stagnation

You were going to remove their graveyard anyway, right? With this a well-timed Bojuka Bog or Relic of Progenitus will end the game.

Mystic Remora

Depending on their deck, you could be drawing a lot of cards. Though I’d be happier playing Rhystic Study if it wasn’t an $8 common.

Necra Sanctuary

A quick clock, minus the creature. Very nice with Wildfield Borderpost.

Necromancer's Covenant

A nice finisher if you set it up through milling or attrition, and don’t forget that last line. Your life swings will be downright Baneslayer-esque.

Null Profusion

This made the list because Recycle costs 50 cents. Amazing so long as you can deal with the dreaded two-land hand. This plays a lot like Future Sight, a 25-cent card that doesn’t qualify as jank.

Orim's Thunder

This one barely qualifies as jank. Enchantment and artifact hate is very important in Singleton formats, and this one should also take out on their creatures. Not bad for a 4 mana instant.

Parallel Thoughts

Maximize your value here by exiling cards that all do one thing, like removal or card draw. Or counters to protect it. But only picking one kind of card can turn this into a super tutor, if that makes sense.

Personal Tutor

A one-mana tutor for a sorcery that only costs 20 cents. This isn’t jank, this is just Masters Edition. I use this mostly to set up a next-turn Wrath of God or Damnation.

Primitive Etchings

Another card that’s better with some sort of library manipulation. Reminds me of the (Sensei’s Divining Top) / Dark Confidant combo.

Puca's Mischief

I love cards that let you be clever, and I love beating my opponent with their own creatures – probably because they’re always much better than mine. Remember than you always just trade their best 4-mana creature with the (Puca’s Mischief) itself.

Pursuit of Knowledge

“Draw seven cards.”

Reach of Branches

Though not the best way to spend your turns, this interesting take on Retrace lets you play the land instead of throwing them out. Lots of card advantage here in a Forest-heavy deck, since it attaches a 2/5 creature to every Forest you draw.

Riptide Shapeshifter

Sort of a poor man's Oath of Druids, but remarkably flexible since it allows you to play with more creatures than just Progenitus and Emrakul, the Aeons Torn in your deck. The key is to just play one Eldrazi or one Hydra with the rest of your creatures, then use Riptide Shapeshifter as your Oath of Druids or Polymorph whenever you draw it. And make sure you include some silver bullet answers like Duplicant (creature type Shapeshifter), Woodfall Primus (Treefolk Shaman), Acidic Slime (Ooze), or Angel of Despair (angel), though I assume you already were. If you get to use it, Riptide Shapeshifter is an amazing card.

Rise/Fall

Rise is a fantastic (and cheap) tempo card that would probably cost a mana more if you weren’t forced to have a creature in your graveyard in order to use it. Fall is less useful until you’ve almost run them out of cards in hand, but the fact that it’s tacked onto Rise as an alternative spell is phenomenal.

Sacred Mesa

I’m partial to this card since it was one of my main finishers both of the years I top-eighted States, but it’s a great way to dodge mass removal or just creature removal in general. 

Scourglass

Not quite a budget form of (Nevinyrral’s Disk) since you typically do want to kill their artifacts as well, but other than that this isn’t bad as a conditional and slow Wrath of God that also hits Planeswalkers.

Shared Fate

Because sometimes you really just want to play someone else’s deck.

Sigil of the New Dawn

This can be expensive, but will reap big card advantage. Evoke your Mulldrifter or Shriekmaw every turn?

Skyship Weatherlight

Would you pay 8 mana to tutor up one artifact or creature? Like Parallel Thoughts you’re probably best planning out your exiles carefully to maximize the value of your random draw, and mitigate the danger of losing all your threats should Skyship Weatherlight be removed.

Stunted Growth

I never knew this card existed until someone played it against me recently and ruined my weekend. I’m a little torn with this one. It basically says “Your opponent just mulliganed to four”, but that kind of effect doesn’t belong in the casual room. Still, if you want the best (worst?) discard effect green has available, this is it.

Supply/Demand
A lot of little dudes or a three-mana tutor. The wide range of multicolored options available in the format can make this pretty close to a Diabolic Tutor.

Symbiotic Deployment

The green Lich. This one is very dangerous if you don’t have a way to get rid of it, since a Wrath effect that catches you off guard will end the game.

Synod Sanctum

This was much better when damage still stacked, but it’s still fun to abuse with EtB-effect creatures.

Taj-Nar Swordsmith

It’s not just a tutor on a stick, it also puts your Sword of Light and Shadow into play. Though you’re still better off with Godo, Bandit Warlord. But this guy will do the trick if you're not playing red.

Tawnos's Coffin

Use it in a pinch to remove one of their creatures and return it tapped for your counter attack. But you’ll get the most mileage from blinking your EtB creatures, maybe drawing 2 from Mulldrifter every turn, or popping something with Acidic Slime.

Thada Adel, Acquisitor

I’ve loved using this one recently. Though like Acquire you’re likely just to hit a (Sensei’s Diving Top) or Solemn Simulacrum before they kill the Acquisitor, that’s often enough.

Thelonite Druid

Rude Awakening on a stick. Can be easier to use than Jolrael, Empress of Beasts, though her effect is a little bigger.

Thought Dissector

I’d love for this to be better, but it’s usually just a bad mill effect.

Thran Tome

Even though you’re not getting the best card of the three, you’re still drawing two cards for 5 mana every turn.

Timesifter

Titan's Revenge

Even just the chance of regrowing a fireball is often good enough, and worth the extra mana.

Tower of Fortunes

Perhaps the best of the Mirrodin Towers, resolving this surely means bad things to come for your opponent.

Traveler's Cloak

Make your biggest beater unblockable and draw a card.

Twisted Justice

This card requires some setup, and you don’t want to draw one card off their dead saproling token. Scarily good when it works.

Tyrannize

Sometimes you’ll deal 7 damage for 5 mana, and others you’ll spend 5 for them to discard two land.

Vengeful Rebirth

Get your best card back and kill one their guys. Fantastic in a format that isn’t dominated by quick, inexpensive spells like Standard and Extended.

Vivify

Cantrip effects always intrigue me, especially when they combo well with other things your deck is doing. The way this interacts with utility lands, yours or theirs, leaves this one wide open.

Wand of the Elements

In longer games sometimes all you need are extra bodies. Obviously very good with Crucible of Worlds.

Wargate

Mana-intensive but amazing. What kind of answer do you need right now? Planeswalkers are always nice, but so is something as simple as a utility land like Volrath's Stronghold. Wargate is the cheapest way to accelerate your mana with nonbasic land in Magic.

Wild Ricochet

My favorite use of this so far was when I shanghaied and copied a Browbeat. But even targeting a Lightning Bolt targeting one of your creatures and sending it back at two of theirs is a three-for-one.

Worldpurge

No no no, let’s start again…

Guided Passage

I’ve played this in Commander for quite some time and love it. Three cards for three mana is a good deal, even when your opponent gets to choose them. Well worth the 77 cents on mtgotraders.com.

Temporal Manipulation

It’s exactly the same card as the $17 Time Warp but with a different name, and at only 60 cents.

Thalakos Deceiver

He’s a little fragile, but for 30 cents you get a Mind Control on a stick. This is significant because it’s much easier to return creatures from your graveyard to your hand than any other card type, so with graveyard recursion cards like Disturbed Burial (a fantastic card) you can conceivably steal their best creature every other turn.