This is correct. You CANNOT copyright game mechanics. Nor can you trademark them.
You CAN, however, own a patent on them. For example...
US Patent 5,662,332
Provided herein is a novel method of game play and game components that in one embodiment are in the form of trading cards (10, 12, 40, 42, 44, 48, 54, 60, 64). However, the game components may take other forms, such as a board game, or the game may be played in different media, such as electronic games, video games, computer games, and interactive network. In one version, the game components comprise energy or mana cards 40 and command or spell cards (10, 12, 42, 44, 48, 54, 60, 64) having commands or spells associated therewith that utilize the energy to enable a player to attack, defend and modify the effect of other mana cards, spell cards, and the fundamental rules of play. The goal of the game is to reduce the life points of other players to a level below one. In this game of strategy and chance, players construct their own library of cards, preferably from trading cards, and play their library or deck of cards against the deck of cards of an opposing player. Cards may be obtained from retail outlets, trading with other players or collectors, and winning cards at games and tournaments.
Translation: This is the patent for Magic: the Gathering held by Wizards of the Coast, currently a company owned by Hasbro. It has been used by WotC to file lawsuit against other companies such as Cryptozoic Entertainment and Hex Entertainment (Case 2:14-cv-00719, filed 5/14/14 in US District Court in Seattle, WA) for producing a game called Hex: Shards of Fate that they feel has duplicated Magic: the Gathering's mechanics, style, and storyline.
It is possible the patent expired last year. I'm not amazingly clear on what renewal laws are possible when it comes to patents but, generally, they expire after twenty years in the US.
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Of course, the thing about protecting patents, copyrights, trademarks, and other forms of legal ownership is to do so requires lawyers and, often, filing motions and lawsuits. Those can be very expensive. More than one company has drowned themselves into insolvency trying to perform or protest such an action. A good lawyer can keep a case tangled up for years if not decades.