Nostalgia

Nostalgia was a deckbuilding mechanic designed for Time Spiral. It was never released.

Description
The idea was the card say that if it was in your deck, then you were allowed to have up to four copies of a card from the past in your deck even if that card wasn't normally legal in Standard. Understanding that those cards might be broken cards, Mark Rosewater found six subsets of past cards, one for each color and one artifact, that could work.

When the mechanic threatened to make deckbuilding legality too complex, Rosewater converted into the un-keyworded gatekeeping mechanic, where you could copy, or play token copies of Vintage-legal cards of the given subsets. This version was also eventually nixed.

The six designed cards were:

Nostalgic Veteran Creature  Soldier 2/3 Vigilance Nostalgic – 2/3 (As long as this card is in your deck, you may have up to four copies of any 2/3 creature legal in Vintage.)

Nostalgic Wizard Creature  Human Wizard 1/2 undefined: Draw a card, then discard a card. Nostalgic – Wizard (As long as this card is in your deck, you may have up to four copies of any Wizard legal in Vintage.)

Nostalgic Zombie Creature  Zombie 3/1 : Regenerate CARDNAME. Nostalgic – Zombie (As long as this card is in your deck, you may have up to four copies of any Zombie legal in Vintage.)

Nostalgic Bolt Instant CARDNAME deals 2 damage to target creature or player. Nostalgic – (As long as this card is in your deck, you may have up to four copies of any card with mana cost  legal in Vintage.)

Nostalgic Beast Creature  Beast 5/5 Nostalgic – Beast (As long as this card is in your deck, you may have up to four copies of any Beast legal in Vintage.)

Nostalgic Artifact Artifact ,undefined: Target player draws two cards. Nostalgic – (As long as this card is in your deck, you may have up to four copies of any card with mana cost  legal in Vintage.)