Learn Swedish: Bedragaren låtsas vara en rik miljonär. - The con artist pretends to be a wealthy millionaire.

The verb låtsas (to pretend) can take a "bare infinitive" (an infinitive without the word att) when the subject of both verbs is the same. Since the con artist is both the one pretending and the one being the millionaire, we can drop the att and just say låtsas vara.

Could I use an att-clause here instead?

Yes, absolutely. You could say Bedragaren låtsas att han är en rik miljonär (The con artist pretends that he is a wealthy millionaire). Keep in mind that you must use this att-clause structure if the subjects are different, such as Han låtsas att hon är rik (He pretends that she is wealthy).

Låtsas ends in an -s. Is this a passive verb?

No, låtsas is a deponent verb. This means it always ends in an -s but has an active meaning. The action isn't happening to the con artist; he is actively doing the pretending. Other common deponent verbs you know include hoppas (to hope) and minnas (to remember).

How do I change låtsas into the past tense?