So how do you identify what are good cards to invest in? Foils of cards good outside of Standard are usually good investments. So if they are still in demand, the best way is to check how high vendors are willing to pay for them in cash.
Here’s 5 cards you should keep your eye on from Khans of Tarkir:
The Impersonator is the most played card outside of fetch lands in EDH (Commander). It's probably one of the best clones in Magic history. It saw Standard play, but not enough to really move its price. The demand is all Commander, really, so it's likely to be reprinted in some future Commander product. Still, this makes foils safe investments.
Infect is the primary deck in Modem that uses this card. But there are others. It's probably the best pump spell in the history of Magic. While foils always aren’t cheap, it’s highly unlikely that we see this in a Standard-legal set again anytime soon, especially because it has Delve on it. Could it be in some future Modern Masters supplemental set? It’s possible, but that will be years down the road.
In the right deck, this is almost always a one-mana Negate. And if your opponent is tapped out, the Ferocious doesn't even matter. It's been Standard playable for good reason. It does see a good amount of Modern play already, so this is a safe place to park a few dollars. Like Become Immense, it may be in some future Modern Masters product, but having the keyword Ferocious on it will limit where it can be a lot.
People want this card in playsets. The deck has fallen off a bit in Modern and it never took off in legacy. However, with Ancestral Vision legal in Modern now, the deck may get the card it needed to be more consistent. The regular version is a great buy, but there are far fewer foils available. It’s an enchantment that benefits you to have multiple copies on the board, so people will want 4 foil copies for their decks. Due to the built-in need to have the full playset, it will go up much much faster and stay higher long term.
OK, this is sort of cheating, but seriously, you can’t go wrong here. Obviously, the fetchlands are good in Modern, Legacy, Commander, and really anywhere that's not Standard. They are always in demand. The foils are already expensive. But they aren't getting cheaper. Also, the Zendikar Expeditions held down demand to the point that these foils really haven’t risen at all.
Considering how high the original Onslaught printings of the fetches became, the sky's really the limit here. Could they be reprinted in some supplemental set? That’s certainly possible. But as we’ve seen, there’s enough demand that long-term these are probably still great investments.
In order of most to least valuable: Polluted Delta, Flooded Strand, Windswept Heath, Wooded Foothills, and Bloodstained Mire.
We’ll be looking at foils from Fate Reforged next.