Learn Spanish (Latin America): Ese transeúnte estará disfrutando la mímica un ratito. - That passerby is probably enjoying the pantomime for a little while.

This is the future of probability. In Spanish, you can use the future progressive (estará plus a gerund like disfrutando) to make a guess about an ongoing action happening right now. It translates to 'must be enjoying' or 'is probably enjoying' rather than something happening in the actual future.

Why isn't there a word for 'for' before un ratito?

While English normally requires 'for' in the phrase 'for a little while,' Spanish frequently omits the preposition por when stating how long an action lasts. You can just attach a duration phrase like un ratito directly to the rest of the sentence.

Since transeúnte ends in '-e', how do we know its gender here?

Nouns referring to people that end in -nte often use the exact same form for both masculine and feminine. The masculine adjective ese (that) is our clue that this specific passerby is male. If it were a woman, it would be esa transeúnte.

Does la mímica refer to the mime artist or the performance itself?

La mímica refers to the performance, meaning the pantomime, gestures, or mimicry. If you want to talk about the actual street artist performing the mime, you would use the word el mimo or la mimo.