> For the complete documentation index, see [llms.txt](https://whitepaper.spellfire.com/spellfire-whitepaper/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://whitepaper.spellfire.com/spellfire-whitepaper/spellfires-gameplay/rule-of-cosmos.md).

# Rule of Cosmos

The rule of the Cosmos ensures, only one of each champion, artifact, realm, and holding card can be in play at a time. This means that a player's opponent cannot have the same card in their pool or battle.

Same cards, even if they are upgraded, cannot be played. Whether a realm is razed or not, it remains in play, preventing other players from playing the same realm into their formation.