is it bad to put two cards in one sleeve 1000 Pack Card Sleeves, 500 Matte Trading Card and 500 Inner Sleeves Ideal for Double-Sleeving, Fit for MTG, TCG and Game (5 Colors) : Toys & Games Double Sleeving worth it? :

One of the unique features of the game board is a built-in mechanic that takes the place of needing dice or coins to flip

They are commonly used for Commander, cubes, kitchen table games, and unsanctioned events when the group or organizer allows them

Magic: The Gathering X Final Fantasy Reveals an Amazing Set of New Commanders Wizards of the Coast teased both Magic: The Gathering and Final Fantasy fans by showing a few cards of their upcoming Magic: The Gathering X Final Fantasy set

It's also a good way to keep things tapped if you have creatures that want to stay tapped but don't want to swing in, maybe like Pain Seer if you're a sicko like me