Archwing Dragon – Avacyn Restored rare. The mountains of Stensia are a treacherous place to go exploring, as the travelers in the lower left of the Archwing Dragon illustration are learning.
Runeboggle – Guildpact common. When Runeboggle resolves, its caster gets to draw a card even if the controller of the targeted spell pays . However, if the targeted spell gets countered by something else before Runeboggle resolves, Runeboggle itself will be countered for having no legal targets, and its controller will not draw a card. Did you follow that?
Scrabbling Claws – Mirrodin uncommon. When Scrabbling Claws was printed, it was very similar to Phyrexian Furnace, which already existed. But the Phyrexians didn't exist on Mirrodin, so a new card had to be made. But when Scars of Mirrodin came out, the Phyrexians got to Mirrodin after all.
Standardize – Onslaught rare. When Standardize was printed, the creature type "Wall" still had rules baggage that kept creatures from attacking. Since then, that effect has been moved to the keyword "defender," so Walls can now technically attack. But Standardize still has its restriction!
King Suleiman – Arabian Nights rare. In Arabian Nights, there was a four-card cycle of Djinns and a four-card cycle of Efreets. Neither cycle had a white card, presumably because King Suleiman was holding them off. To this day, the only Djinn or Efreet in white is Ruham Djinn in Invasion. (If you don't count Changelings.)
Brassclaw Orcs – Fifth Edition common. The flavor text for the Fifth Edition printing of Brassclaw Orcs mentions Sarpadia. This is a reference to its original appearance in Fallen Empires, where three of the four versions of the Orcs (here, here, and here), quoted Sarpadian Empires, Vol. IV. The fourth one, which doesn't mention Sarpadia, has the illustration that made it into Fifth Edition.
Platinum Emperion – Scars of Mirrodin mythic rare. Platinum Angel first appeared in Mirrodin and it said this: "You can't lose the game and your opponents can't win the game." When Magic returned to the plane in Scars of Mirrodin, a new platinum creature was called for. And Platinum Emperion fit the bill!
Gisela, Blade of Goldnight – Avacyn Restored mythic rare. Gisela is the leader of Flight Goldnight and was one of the few witnesses to the battle between Avacyn and Griselbrand. Her despair at seeing Avacyn trapped in the Helvault would not go away until Avacyn's return.
Electrolyze – Guildpact uncommon. If you run acoss an Electrolyze that shows someone in a pitched battle in a city street, you've got a special promotional version that came with an issue of the Magic: The Gathering comic book.
Terminate – Planeshift common. According to the flavor text, the Planeshift version of Terminate depicts the death of Darigaaz, the Igniter, when Darigaaz sacrificed himself to save the crew of the skyship Weatherlight. Learn more about Darigaaz's story here.
Predator's Gambit – Avacyn Restored common. The art in Predator's Gambit shows a vampire that has been forced into the position of being hunted, rather than the hunter. But that might not last, because the vampire is getting mad!
Terminus – Avacyn Restored rare. From the Avacyn Restored FAQ: "Each player chooses the order for his or her own creatures. This order isn't revealed to other players."
Descent into Madness – Avacyn Restored mythic rare. From the Avacyn Restored FAQ: "First you choose the permanents and/or cards from your hand that will be exiled. Then each other player in turn order does the same. Then all the chosen permanents and cards are exiled simultaneously. Players who choose after you will know what permanents you'll be exiling when they choose. They'll know how many cards you'll be exiling from your hand, but they won't see those cards."