Learn Farsi: او خارق‌العاده‌ترین ورزشکاری است که در این باشگاه وزنه بزند. - He is the most extraordinary athlete to lift weights in this club.

This is the main point of your current lesson! When a relative clause (starting with که) describes a noun modified by a superlative adjective like خارق‌العاده‌ترین (the most extraordinary), Farsi uses the subjunctive mood. It gives a sense of 'out of anyone who might do this action.'

Why does ورزشکار (athlete) have an ی at the end (ورزشکاری) if we are talking about a specific 'most extraordinary' person?

This is the restrictive ی used to link a noun to a relative clause. Even though the person is specific, Farsi adds this ی to the noun right before the که (who/that) clause. You can think of ورزشکاری که as 'the sort of athlete who...'.

What makes up the verb وزنه بزند?

It is the present subjunctive form of the compound verb وزنه زدن (to lift weights). وزنه means 'weight', and the helper verb زدن (to hit/strike) takes the subjunctive prefix بـ and the third-person singular ending ـَد to become بزند.

خارق‌العاده‌ترین looks like a very long word. How is it put together?

The base word is خارق‌العاده (pronounced kharegh-ol-adeh), an Arabic borrowing that means 'extraordinary.' The ترین suffix is the standard Persian ending used to make superlative adjectives, turning it into 'the most extraordinary.'