Learn Swedish: Du behöver inte låtsas vara godtrogen för att spela med. - You don't need to pretend to be gullible to play along.

When the subject doing the pretending and the action being pretended are the same, låtsas takes a bare infinitive. You just say låtsas vara (pretend to be). If you want to use att, you must use a full clause instead, such as låtsas att du är godtrogen (pretend that you are gullible).

Is låtsas in the present tense or infinitive here?

It is in the infinitive, because it follows the auxiliary verb behöver. Låtsas is a deponent verb, meaning it always ends in an -s but has an active meaning. For this specific verb, the infinitive and the present tense happen to look exactly the same, so you have to rely on the surrounding grammar to tell them apart!

How do you break down the word godtrogen?

It comes from god (good) and tro (belief or to believe), combined with the adjective suffix -gen. It literally describes someone whose belief is too good or trusting, which translates to gullible or naive in English.

What role does med play at the end of the sentence?

It belongs to the phrasal verb spela med, which translates to play along. In Swedish, this is a particle verb, meaning the particle med is the stressed word when spoken. It changes the meaning from simply playing a game to participating in a charade or a joke.