This old school Legends card is a tricky way to reanimate creatures from all graveyards. Timed correctly, it can do a lot of work. The format you would expect to see it in most, however, is Commander, and there are simply better options for mass reanimation. Liliana Vess and Rise of the Dark Realms give you control of all creatures, for example.
The real interest in this card is primarily due to its inclusion on the Reserved List, meaning that it can never be reprinted. Collectors love this card for its subject matter, artwork, and rarity. It's a cool card to have, and its price shouldn't be coming down anytime soon.
Attrition has been a popular Enchantment in EDH/Commander for quite a long time. With the release of the popular new Commanders Mazirek, Kraul Death Priest and Meren of Clan Nel Toth, The Commander 2011 printing has been selling out quickly everywhere. Now, the original Urza's Destiny printing is seeing its supply dwindle. This is definitely a card to have if you play Black in EDH at all. If you don't play EDH, there are probably better ways to spend your money, but never hesitate to pick up this card in trade if you happen to see it.
For a card with three different printings, it's somewhat incredible that Awakening Zone has made such a mighty leap in price over the past few months. From Beyond from Battle for Zendikar has actually helped the popularity of this already very useful EDH/Commander card. While From Beyond has the distinction of creating 1/1 tokens rather than 0/1 tokens, it makes sense to play both cards in the decks that want them. It's one of the hottest cards being picked up for the format right now and all printings are a solid pickup as this card probably won't be reprinted any time soon.
One of the stranger price spikes in December 2015 has been Chainer's Edict. Once a very strong card in the competitive scene, it's been relegated to mostly casual play over the past decade or so. Its flashback cost is expensive at 7 mana, but useful. The only reason that this card may have suddenly jumped in price is the fact that the Edict was reprinted at common in Vintage Masters on Magic Online. It's printed at uncommon in paper Magic (and even mythic rare in the From the Vault: Twenty printing).
It's doubtful that Chainer's Edict remains $5 as there seems to be quite a buyout occuring. Many copies of this card probably still exist in the world, so it seems highly unlikely that it can maintain this price long-term. The FNM Promo and From the Vault: Twenty editions are still reasonably priced. This card is fine to pick up in foil, certainly, but Pauper doesn't really see a lot of competitive play in paper. It's more likely that Cube players are the culprits for the Torment editions suddenly being bought out. Steer clear of the nonfoil editions and focus on the foil printings - including the Torment version.
The hybrid Blue/Green Enchantment has seen an organic jump in demand for one reason only: Commander 2015 Legendary Ezuri, Claw of Progress. The synergy with Ezuri's ability to gain you an experience counter whenever you have a creature with power 2 or less enter the battlefield is extremely powerful. This isn't a card you would expect to see reprinted anytime soon, either. Foils have already jumped from $6 to $20. The nonfoil should not be far behind.
Fable of Owl and Wolf is probably good in other Blue/Green Commander decks, but Ezuri, Claw of Progress and the Fable are perfect for one another. Once this card is gone, it's hard to say how many more copies are out there.
The Spiritdancer, originally printed in Rise of the Eldrazi, has seen her limited Planechase printing's price fluctuate erratically. She sees play in one Competitive Modern deck, Green/White Auras - better known as Bogles. There are still enough Rise of the Eldrazi copies out there that there shouldn't be a price spike anytime soon. However, if Bogles Top 8 a Modern Pro Tour in the near future, since Kor Spiritdancer is played as a four-of in the deck, there could be a huge price jump, especially in the rarer of the two printings.
It's highly unlikely that the Spiritdancer's price will drop. She is playable in some Commander decks, too, and Bogles probably aren't going anywhere as a Tier 2 Modern deck that can occasionally finish first with a strong pilot and a bit of luck. If you can secure copies under $10, they are certainly worth having. Kor Spiritdancer is a safe investment, but the Rise of the Eldrazi printing is probably the better buy.
Any Commander deck that runs a fair amount of basic lands wants Myriad Landscape. With the spoiling of the sixth basic land being featured in Oath of the Gatewatch, Wastes, that taps for colorless mana, there's been a huge spike in demand for the Landscape. This was a $2 card not that long ago, and now it's pushing $5. The time to buy-in for profit has probably passed, but if you need copies, it's not a bad idea to pick it up. Then again, this card could easily be reprinted in any set, as it's hardly limited to Commander. Were it printed in a Standard/Modern legal set, it could definitely see play. Unless you need copies for your EDH deck right now, though, it's probably best to steer clear.
Portal Second Age is a pretty rare set at this point, and it's not exactly chock-full of a ton of expensive cards. While there are hits in the set, Predatory Nightstalker is a card exclusive to the set that's relatively underpowered. While hardly terrible, it's not a card you'll see played much anywhere. But because it's so exceedingly rare, it seems like a solid card to hold onto.
While not a card we would recommend as a buy, it's unlikely Predatory Nightstalker will be reprinted. The effect is actually half-way decent - force your opponent to sacrifice a creature when it is cast from your hand. But there are more cost-effective ways of doing that, although coming along with a 3/2 body is not nothing. There's just no deck that would play this card over something like Chainer's Edict.
While not a widely played card, Sphere of Resistance does see competitive play in Legacy and Vintage. While neither format is as popular in paper Magic as it once was, the Sphere is from an old enough set that there aren't many copies left on the open market. It's seen some wild price swings in late December. While this isn't a sure-fire bet for profit, it sees some fringe Commander play. It's also unlikely that the Sphere will be reprinted, although it's not impossible.
With the announcement of the Stoneforge Mystic Grand Prix promo, there is mounting sentiment that the Mystic will be unbanned in Modern. Currently, the Mystic only sees play in Legacy and Commander. Stoneforge decks are also not as prevalent in the Legacy format as they once were. So there's a lot of upward pressure on the Mystic right now. $40 seems a bit high for a card that may not even be unbanned, so it's a card to watch, but it seems prudent to be selling copies into the hype. This is a bit too high of a buy-in to guarantee any real profit if the Mystic isn't unbanned in Modern. If you want to take the risk, and the Mystic is made legal in the growing Modern format, then it could be worth it.
Sylvan Library has seen a lot of growth in its price over the past couple of years due to its extreme popularity in Commander. While the Library does see some Legacy play, Commander is the format that's fueling most of the demand. The Legends printing is the most active right now, but its other printings in Fourth and Fifth Edition are still good pickups. There's also a Commander's Arsenal foil printing over $100.
With the possibility that Sensei's Divining Top will one day be banned for being generally un-fun to play against in both Legacy and Commander, the Library is in a position to see even more play than it already does. The card filtering it offers is extremely good, plus it can actually draw you extra cards at the cost of 4 life for each card - a fairly high price, but it can be well worth it.
Easily the best of the 5 "tempting offer" cards from Commander 2013, Tempt with Discovery is seeing its supply dwindle. While it's possible for this card to be reprinted in a future Commander or multiplayer product, being part of a 5-card cycle makes that someone unlikely. With Omnath, Locus of Rage decks all the rage in Commander right now, it's not hard to see why this card is so hot right now. It's definitely worth grabbing as it's played in a wide array of EDH decks.
Another of the cycle to keep an eye on is Tempt with Vengeance. It's still extremely cheap, but sees play in Omnath, Locus of Rage and other popular decks. The other three, while each useful in its own right, simply don't have enough demand to raise above bulk status right now.
Due to Tron being one of the top decks in the Modern format, the three Urza "Tron" lands are always popular. In particular, the original Antiquities printings tend to be very interesting financially. There are huge peaks and valleys for each of the lands due to the fact that there are multiple artworks for each of these lands.
While these several artworks also are featured on the white bordered Chronicles printings, the black-bordered Antiquities versions are much more desirable. You can never go wrong stocking up on Urza "Tron" lands, no matter what the printing. Just be aware to be on the selling end whenever there's a spike with any particular artwork and trade accordingly.
One of the more popular Commanders in EDH, Zedruu was under-priced for many years. Due to slowly acquiring some very useful cards for the "donate" strategy over the past couple of years, Zedruu decks have slowly gained more in popularity. It wasn't until 2015 that Zedruu broke $2, and she's been fluctuating between $3-4 since September. It's possible that we could see Zedruu reprinted at some point in a promotional printing, but the Minotaur Monk probably isn't going to be reprinted in a high volume set. If you're wanting to play Zedruu, now is the time to snag a copy of her.