In the past, the main concern was random, expensive, old Reserved List cards, which are comparatively easy to counterfeit
2.0/10$0.72 Pyrrhic Revival Sorcery Each player returns each creature card from their graveyard to the battlefield with an additional -1/-1 counter on it
Then you can discard two cards at the beginning of your first main phase to return this to your hand from your graveyard, which is card disadvantage naturally but with madness, lands, discard triggers like Archfiend of Ifnir, and loads more, it's got value
This is extremely useful when all you have are reactive cards and you need to find more proactive spells: You get to cast whatever you found useful in the 7-card batch, and regain your reactive cards at the end of the turn
You only untap one creature, but thats plenty exploitable with cards like The Infamous Cruelclaw, Roxanne, Starfall Savant, and any other creatures with valuable saboteur or attack triggers you want to get multiple times a turn