This spell has no targets. You don't choose five permanents you control until Clarion Ultimatum resolves. If you control fewer than five permanents at that time, choose each permanent you do control.

The five permanents you choose must all be different. However, some of them may have the same name as one another. For example, you may choose two Empyrial Archangels and three Plains. If you do, you search your library for up to two more Empyrial Archangels and up to three more Plains and put them onto the battlefield tapped.

If you choose a permanent whose name has been changed by an effect (for example, a Clone that's copying another creature), you'll search for a card with the new name, not one with the original name. Note that changing a land's subtype doesn't change its name.

If you choose a permanent with no name, such as a face-down creature, no card in your library can be found with that name.

You make just one search. (This could matter for cards like Aven Mindcensor, for example.)

The cards all enter at the same time. If one of the cards that's entering is an Aura, it must enter attached to a permanent already on the battlefield. It can't enter attached to another permanent entering via Clarion Ultimatum. If an Aura can't enter this way, it remains in your library.

If you find a card that isn't a permanent card while searching (for example, you chose an Illusion token and find the split card Illusion/Reality), that card remains in your library.