Meaning if your cap is 10 cards then will have to decided which 10 cards you would like to use in your battles
I have, however, seen meme decks playing 36+ lands
x2] [When Attacking] (You may rest the specified number of DON
10 Add: The Gitrog Monster Cut: Millikin Were going to go ahead and cut the little mana dork who couldnt in exchange for a big bad Frog who can capitalize on all your land drops
Enter the Infinite, Volcanic Salvo, Apex of Power, Time Stretch, Mnemonic Deluge, Rise of the Dark Realms, Worldfire, most of the game's most expensive, game-winning instants and sorceries are free to her
So if I make my commander Captain America, First Avenger (a red-white-blue creature), I cannot use any green or black cards while building that deck