You can choose a mode only if you can choose legal targets for that mode. Ignore the targeting requirements for modes that aren't chosen. For example, you can cast Ojutai's Command without targeting a creature spell provided you don't choose the third mode.
Atarka's Command
If you choose the third mode and put a land card onto the battlefield, that doesn't count as playing a land. For example, you can both play a land and put a land onto the battlefield this way during your turn.
As the spell resolves, follow the instructions of the modes you chose in the order they are printed on the card. For example, if you chose the second and fourth modes of Ojutai's Command, you would gain 4 life and then draw a card. (The order won't matter in most cases.)
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Chris Rahn
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