First, just because a card has an old frame doesn’t make it exempt from Modern play. Just like any other format, so long as any printing of a card is legal in Modern, any black-or-white-bordered, regular-backed version of that card is legal in Modern. You can rock your Judge foil Crucible of Worlds or Noble Hierarch all day, or your Beta copies of Lightning Bolt. Even the cards that were reprinted in Time Spiral with the purple expansion symbol (still using the old frame) count as being printed in a set after 8th edition! For example, Avalanche Riders has never been printed in a Modern card frame, but is still Modern legal for this reason.
On the flip side, just because a card has a modern card frame doesn’t make it Modern-legal. The biggest problems you’ll run into here are usually multiplayer releases of products like Archenemy, Planechase, Commander, and the like. For example, True-Name Nemesis is legal in Legacy, but is NOT legal in Modern. Neither are not-already-Modern legal cards in the From the Vault sets, like the Lotus Petal from FTV:Exiled.
So what IS Modern legal, you might ask? It’s actually pretty simple: Unless the card is banned (like Bloodbraid Elf!), any card printed in a Core Set since 8th edition, or a regular expansion set since Mirrodin, is Modern legal.
Today’s Tournament Tip written by Trevor Nuñez