When spoilers are first released, speculation about playability in Eternal formats is at its highest. During this time assertions about which cards are likely to impact the most powerful formats fly left and right. It can be difficult to navigate all this contradictory information, but speculators who can cut through the nonsense stand to make profit on misplaced hype.

Legacy is a rare animal and evaluating cards for it can be difficult. When I'm trying to to determine the potential of a new card in Legacy, I look at four basic characteristics:

1. Power -- In order for any card to see Legacy play it either needs to match or surpass the power of an existing card, or provide a completely unique effect.
2. Converted Mana Cost -- The lower the better. While this is important in all formats, it is especially so in one as efficient as Legacy.
3. Pitchable to [card Force of Will]Force[/card]? -- While this obviously isn't a deal breaker, blue cards should be scrutinized more simply because blue is the most powerful color.
4. Similarity to Staples -- Does it do something similar to a card that already sees play (Terminus compared to Wrath of God, Dismember compared to Swords to Plowshares)?

To give you an idea of how I approach these questions, I'll show you my thought process on a few recently-released cards.

Abrupt Decay

1. Power: An uncounterable answer to most of Legacy's powerful cards and the best answer to Counterbalance.
2. CMC: 2 mana (even of different colors) is very efficient for a cheap catch-all solution.
3. Blue or Not: No (But we should be thankful for this. Blue shouldn't get such efficient answers, otherwise its power level would go up even more.)
4. Comparisons: This card mimics Vindicate except at instant speed (though it misses on lands and permanents with CMC above 3). Vindicate does see fringe play and is valued at 30+ dollars.

Final Evaluation: Pick up while cheap. The fact that Abrupt Decay doesn't see much Standard play allows its value to remain depressed as more enter the market, while demand is limited to Eternal formats. This will not last indefinitely.

Supreme Verdict

1. Power: This card is easily as powerful as Wrath of God (a 5+ dollar card.)
2. CMC: The converted mana cost is typical for this effect. Its slightly more stringent color requirements are mitigated by the fact that one of those colors is blue.
3. Blue or Not: Yes, pitch away.
4. Comparisons: Wrath of God was played in older U/W control decks. Supreme Verdict is a strict upgrade and uncounterability is a very powerful effect.

Final Evaluation: Pick up while less then 3.5 dollars. But Terminus is still the superior mass removal spell, due to its low miracle cost and the fact that you'd rather send your opponents' creatures to the bottom of their library than their graveyard.

How about something a little more challenging?

Misthollow Griffin

1. Power: A 3/3 flier for four mana -- pretty awful as a generic creature. However, its ability is very unique (the only of its kind.) It combos well with Food Chain, but unless you already have another more powerful creature in hand, all you can do is create infinite, unusable mana. (It can only be used to cast creatures.)
2. CMC: Four, the same as Jace, the Mind Sculptor. Ask yourself when you would prefer to cast the Griffin instead of him.
3. Blue or Not: Yes. Not only can it be pitched to FoW, it is the only card in Magic that actually eliminates the card disadvantage in the process.
4. Comparisons: Similar to many a generic 3/3 blue flier, none of which see play. However its unique ability has the potential to be broken.

Final Evaluation: I'm currently picking these up in the 50-75 cents range. The risk of loss is only about 25-50 cents per card (mythic bulk price is 25 cents), whereas the break-out potential (and it being a mythic) means it always has the potential to become semi-valuable. Its inherent lack of power does means it isn't good in a vacuum and would need to be coupled with other cards to take advantage of its unique ability.

Turning to Gatecrash

Now that we have established criteria for speculating off of spoilers, let's review a few Gatecrash cards.

Gideon, Champion of Justice

1. When Gideon enters the battlefield he does almost nothing and he can't protect himself. When Legacy decks get lots of creatures out they tend to kill you very quickly (think of Goblins, Elves and Dredge) so his first ability is irrelevant. His second ability does provide a decent wincon with some protection, however not against Swords to Plowshares, the removal spell of choice.
2. The converted mana cost is fine for a planeswalker, but he's in direct competition with [card Elspeth, Knight-Errant]Elspeth[/card] at the same CMC... Except he's much worse.
3. Not blue, can't be pitched to FoW.
4. His abilities, while different, currently have little use in Legacy.

Final Evaluation: Virtually no chance of seeing play in Legacy.

Boros Charm

1. Smacks your opponent for four, makes your permanents indestructible, or gives one creature double strike -- this charm is pretty ridiculous. The power level is up there.
2. A cheap CMC of two, although red and white are rarely paired together without blue. Thanks to Legacy mana bases, though, it's not hard to pay this cost.
3. Not blue, can't be pitched to FoW.
4. This card is similar to Flame Rift in that it costs two and deals four to your opponent (though this doesn't hurt you as well). Making permanents indestructible is currently not done much in Legacy, though that may be because the ability is rare and it has never been available for so little mana. I expect this ability's usage to grow over time as people realize it counters Abrupt Decay and Wasteland. Giving a creature double strike can be brutal in a format dominated by only the most cost-efficient threats.

Final Evaluation: Decent chance of Legacy play. The color combination is currently not seeing much play, but this charm does a whole lot that Legacy hasn't had access to.

Enter the Infinite

1. This card allows you to do something incredibly absurd, which is why it costs twelve mana. Card advantage goes hand in hand with winning, so massive card draw usually comes with a drawback. This card just has an absurdly high casting cost instead to keep it from being played too quickly. Drawing your entire deck (minus one) is typically the desire of a combo deck, because you must win on either that turn or the next. This card was quickly determined to go hand in hand with Omniscience, which would allow you to play it and everything you draw for free.
2. The CMC is twelve, although any deck that plays this has no intention of actually hardcasting it. (Most will cheat it in via Omniscience, but look for other ways as well.) If you do pay the full cost, you probably don't have extra mana to cast all the stuff you draw, so you'll need a (near-)infinite engine to win. This drawback means that its overall value in the long run will probably stay below Omniscience's.
3. Blue, so it can be pitched to FoW.
4. This card is similar to Ad Nauseam. It will only see play in a combo deck with lots of ramp spells or a way to kill the opponents by discarding/exiling cards. It also combos with Laboratory Maniac, which can be triggered after resolving Enter the Infinite with a simple Brainstorm.

Final Evaluation: Decent chance of Legacy play (at the beginning) but I imagine people will just stick to Disciple of Griselbrand as the draw engine of choice, since the same spells that cheat Omniscience into play can also be used with Disciple of Griselbrand. He also provides a solid win condition that can protect himself (by drawing counterspells). All in all, I suggest unloading these early on and picking them back up when they get closer to "bulk" status (i.e. $1-2).