Way, way, way back, I got an issue of InQuest magazine that included a bit where they converted Magic cards into D&D spells, monsters, and such... For 2nd edition. Wow, that really was way, way, way back. Anyway, the concept stuck in my head for a bit, and made a few brief returns when I'd get an urge to be creative with Craft Construct. Anyway, I'm going to list some stuff, and see what some of you can come up with for Magic-to-D&D translations.
Baku Altar: Think I could use something like this for a way villains could make minions.
Basalt Monolith: It's a crappy card, but I like monoliths.
Glasses of Urza: Peek!
Teferi's Puzzle Box: Card store I used to go to had gimmick $2 tournaments, often where an artifact or enchantment was treated as always in play. This was one of the fun ones.
Thran Forge: Roboticize!
Thran Turbine: Arcane engine of some sort?
The Arcbound Critters. I like the idea behind the Modular power.
Assembly Worker: Critters that support one another.
Chronatog Totem: My sand wizard is thinking of expanding some stuff into time magic. Like sands through an hourglass.
Darksteel Brute: You know, I kind of like stuff in Magic that's not a creature, but becomes one on demand.
Jhoira's Toolbox: A cute robotic bug that carries tools in it. Hmm...
Loadstone Myr: Hmm... Maybe a character can use one of their daily item powers to give it a boost?
Mobile Fort: Hmm... Mobile base of operations.
Onulet: Another gimick tournament critter that showed up: Gimmick was that players would start with random artifact creatures on their side. I got this one.
Triskelavus: Flying machine with detatchable fighters?
Wall of Junk: Might work as a defensive spell.
Workhorse: Equine golem trading its strength for magic. Hmm...
Yotian Soldier: No idea why, but I like this critter. Think I've only played it once, when I was learning.
Anyway, that's the Magic stuff. While you're here, like some thoughts on some magic items and possible artifacts.
3 big honking pearls: Sacred treasures for three isolated tropical islands. No idea what sort of powers they should have. Tied in with some bloodsports they played centuries ago in competition with each other for glory.
Efreet Ring: Bit more detail on this one in my mind. It's one of a group of rings made by master goldsmiths, topped with rubies shaped into flames. Each holds the spirit of a manipulative efreet who gives advice to the wearer that usually leads to backstabbing if followed. Those who ignore this advice sometimes end up as piles of ash. These rings are more or less minor artifacts.