Welcome back readers and speculators! I usually do a piece on the "legacy" of a new set, highlighting the cards I think will have an effect on the Legacy format; today I will expand that to include Modern as well. Unfortunately "The Eternality of M15" just sounds weird to me, so we'll stick with the legacy and ask you to accept that it does in fact include Modern notes. My criteria is as follows;

1. Does it fit into an existing archetype?
2. Does it create a new archetype?
3. Does it pitch to Force of Will (i.e. is it blue, and this is only relevant for the actual Legacy picks)?

Pretty simple grading criteria. I will skip a majority of the cards who are clearly not Legacy/Modern caliber and I'll just focus on the ones I feel might find a home. I'll also ignore reprints that already see play in either format.

1. This is a strict upgrade for Elves players. They just remove their Viridian Shaman, swap in this guy, easy peasy.
2. Nope.
3. Nope.

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I wrote about this guy in pretty good detail (found here).

1. This guy is likely to find a home in Modern (most likely as an answer to Birthing Pod value decks and Splinter Twin decks), as Modern already has people playing Torpor Orb. However, Legacy does not. He already fits into the G/W Hatebears shell quite nicely with his brother Aven Mindcensor to really put the hurting on value creature-based decks.
2. Nope.
3. Nope.

1. Meathooks is a deck. It's not a Tier-1 deck, but a "rainbow land" with no downside that also makes creatures that will likely have a lot of abilities for five mana is pretty impressive. Meathooks has always suffered the same problems that all creature based decks do in Legacy, which is that they rely on several creatures to win, thus they are often forced to overcommit to the board, putting them in situations in which a single mass removal spell puts them way behind. Having a land that can create the creatures adds a lot to mitigate this issue. The cost of making the slivers is high, but this allows the deck to only commit one to two creatures to the board and simply starting pumping out uncounterable tokens to provide a threat, thus reducing their card disadvantage to a wrath effect.
2. Nope.
3. Nope.

1. As stated above, Slivers are a Legacy deck. Currently they have Crystalline Sliver for a better version of Diffusion Sliver's ability, however they can only run 4x Crystalline and depending on how much spot removal is popular in the format, this ability may be critical for the deck's stability.
2. Nope.
3. Yep.

1. Again... Slivers are a Legacy deck. Two mana to basically add a Hellrider ability is really good in a deck that swings with quite a few creatures quickly. The fact that the ability triggers before damage can help you kill an opponent at low life who happens to have a lifelinker (say Batterskull or Disciple of Griselbrand) before the lifelink activates.
2. Nope.
3. Nope.

The Maybes

These are the cards that might find a home, but they would likely serve as either the fifth copy of a better spell or require not only a new archetype, but likely another similar spell to make the archetype viable.

1. Never underestimate one-mana removal. This card is similar to Dismember in black's arsenal of cheap kill spells (though unlike Dismember you can only cast it if you are playing black). The downside for this one is not only do you have to pay a colored mana, but you're trading three life for -3/-3 compared to four life for -5/-5. I don't think it'll ever fill in for Dismember, but it is cheap and kills a lot of the powerful creatures in Legacy.
2. Nope.
3. Nope.

1. This could find a home in some Modern Tron decks, though the ability to exile as opposed to destroy may or may not really be worth the extra mana cost up front (the activation cost is the same as on Oblivion Stone). While Modern doesn't really have any strong graveyard-centric decks like Legacy, this card does permanently eliminate persist creatures, and Tron does have some difficulty beating a resolved Glen Elendra Archmage (especially if they can use Gavony Township to negate the -1/-1 counters).
2. Nope.
3. Nope.

I know a lot of people want this to be good and it is quite powerful.

1. This card could find a home in some form of an updated Zombardment deck (basically a RBw deck that uses recursive creatures to generate card advantage and grind out the opponent). The fact that it makes zombies gives it synergy with Gravecrawler and it does eliminate one of the biggest issues with black style hand control decks. Tacking on something else to your late game discard spells (especially a cantrip) makes them a whole lot better. This card plays really well with Liliana, potentially allowing you to turn her first ability into actual card advantage, even when your hand isn't empty already. I know a lot of people who are trying to break this card. Personally I'm a bit more bearish on it than bullish, but it wouldn't surprise me to see it make some waves.
2. Nope.
3. Nope.

1. This doesn't fit into any existing archetypes currently.
2. This does seem like an engine card, by which I mean it does have a very high power level and drawing multiple cards for no mana is an ability we've seen broken many times (Necropotence, Yawgmoth's Bargain, Griselbrand). This is an interesting take, though unlike the three I just mentioned, instead of using life as the card drawing resource, we are using our lands which are far more finite in a game. The life cost ones also don't also restrict you from gaining the resource back, whereas Aggressive Mining shuts off further land drops. A CMC of four also seems to put it at a pretty big disadvantage, after all, if I'm paying four mana in Legacy I want JTMS or Sneak Attack.
3. Nope.

Ætherspouts

1. This card is hard to analyze. On one hand, the decks most likely to play this (i.e. control decks) already have Supreme Verdict and/or Wrath of God for removing multiple problematic creatures. The fact that it gives your opponent options usually has it destined for the bulk bin. However I would be remiss in my duties if I ignored the fact that while it does let your opponent get access to his good creatures it does force them to draw them and play them over again. Controlling the top of your opponents deck can be huge, especially when you know they need an out to something. Rather than focus on those magical christmasland scenerios though I simply thought it wise to mention this card and that it is quite powerful.  I consider this an upgraded Evacuation in all but a few scenarios (basically the ones in which you need to eliminate a creature they didn't attack with).
2. Nope.
3. Yes, though I don't know if this is truly Legacy caliber (it would be better in Modern where creature-based decks are far more common).

And Now for the "More"

A friend of mine was visiting a flea market when he came across a vendor who had Magic cards. After verifying that the cards were 12 for $1, he proceeded to pull out a few goodies. Mainly:

As well as 21 Unglued lands, some Brainstorms, and other Legacy commons and uncommons. To add more to his good luck he returned to the market the next day and the guy had some more cards. He checked the first two cards in the first box...

"Sick story bro, thanks for sharing". So for $27 he got 1x Temporal Manipulation, 2x Wastelands, 21x Unglued Lands, and a plethora of Legacy commons and uncommons.

This wasn't me (I promise) but a friend of mine, and it's not meant to act as a brag--rather it's a reminder that there are many outlets outside of card shops that may have MTG cards and the more obscure they are the more likely they are to have hidden gems for you to pick up. So the next time you find yourself at a flea market, thrift shop, bazaar, auction, etc.  it doesn't hurt to keep an eye out for MTG cards. Who knows, maybe you'll get this lucky...