Welcome back readers! We now have the full M14 spoiler out so I guess we should delve into it.
WoTC has made quite a few interesting decisions regarding M14. They brought back a few high-dollar Legacy cards as well as a couple of obvious casual/EDH cards that have been hard to find.
This actually mimics M13 a bit. M13 brought us Gilded Lotus, Nicol Bolas, Planeswalker and Akroma's Memorial, all cards that had a medium price tag ($10-$20) simply due to strong demand and a smaller print run. It seems Wizards kept the trend going and is giving casual players Darksteel Forge back. I expect its price to drop from a previous $12 to around $4-$6 (similar to Akroma's Memorial) as both are/will be mythic rare and were solely propped up by the casual demand.
Looking over the spoiler the only cards that I see that will affect Legacy are the reprints of Scavenging Ooze and Mutavault and their effect will simply be to drop the price of these card (as they already have.)
Despite a lot of us expecting it, WoTC did not reprint Thoughtseize in M14, instead giving us back Duress. This will most likely result in a spike on Thoughtseize as players pick them up in preparation for Modern season. The only stipulation would be if they are spoiled early enough in Theros that panic doesn't set in from those who sold out expecting to buy back (or basically sold short).
Another interesting reprint, A-Buy Your Silence, will continue to grace combo sideboards from time to time.
I know quite a few of my fellow QS writers would like Tidebinder Mage to be good. Honestly I don't see him as more than a sideboard card in Legacy Merfolk--which currently has been pushed to tier two status, though I think it could have a resurgence.
Now, he could play a more pivotal role in a Modern merfolk deck, especially given he's really good against Jund decks. He serves more as a tempo play to stall or slow down the opponent than as an actual removal spell. I liken him to Vapor Snag or another bounce spell as a good way to stall a threat.
This guy could be used in the Zombardment deck, though it's doubtful. It's important to note that if you have a way to reduce the cost of Tenacious Dead's ability by one colorless you could create an infinite loop with Phyrexian Altar. However, being an uncommon there's not a strong likelihood this card could break $2 even if it did permit an infinite combo.
This may very well find it's way into the Zombardment deck as a worse (but cheaper-to-cast) Goblin Bombardment--perhaps as Bombardment #5-6.
Something to watch as well. If it had haste it would definitely be Legacy material. However, first strike has proven itself a useful ability. It can also serve as an amazing kill card against decks that run a lot of cantrips (Brainstorm, Aerial Responder, Preordain). It's sad that he had to cost double red as this severely limits his splashability.
Another of my "to-watch" cards and one that I will be actively seeking in foil. I think this card will see Legacy play, possibly in RUG decks and definitely in any mono-red aggro/burn decks.
The ability is very powerful and the fact that they don't die at end of turn means that he can fog quite a few creatures every turn, all the while swinging for 2. I can see him being excellent in the RUG vs. RUG matchup as sticking him will supply the owner with a continuous onslaught of creatures. How much dumber is Brainstorm when in addition to all the usual shenanigans it comes with a free 1/1?
Llawnowar Elf, but not exactly (it has different flavor text) and you can run four of each in your Elf deck. Given we already have Fyndhorn Elves to fill the same role, it's unlikely that this makes Elves good in Legacy again.
Modern is a different animal. Modern Elves would now have access to sixteen turn one mana ramps (counting BoP). Maybe target foils, but again I don't see this being big.
Insist 2.0, except instead of drawing a card your creature gets flash and a +1/+1 counter. I personally think this is just a worse version of Insist, but the flash part will probably cause people to experiment with it.
Unfortunately, Legacy decks that would run this don't really need the ability (Elves, Nic Fit). RUG may want it as a way to force your opponent to tap out on his turn.
I would be remiss if I failed to at least mention this card, as it offers a unique ability and is fairly costed. I could see this card creating a new archetype, but whether it will be good depends on the deck builders/tweakers.
Finally, the new Wasteland wannabe. It will most likely prove far more popular in EDH (for those who like cheap semi-replacements) and has virtually no chance in Legacy. In Modern it will compete directly with Tectonic Edge, to which it's pretty inferior. However, I can see it tag-teaming with Tectonic Edge in some sort of fringe LD deck.