Learn Icelandic: Úrvalið er gott og þeir selja ýmsar plötur hér. - The selection is good and they sell various records here.

The word ýmis (various) declines just like an adjective to match the noun it describes. Here, it describes plötur (records). Because plötur is feminine, plural, and in the accusative case (as the object of the verb selja), ýmis takes the feminine accusative plural form ýmsar.

Wait, what happened to the second 'i' from ýmis in the word ýmsar?

When you add an ending that starts with a vowel to ýmis (like the -ar ending for feminine plural), the second i in the root drops out to make it easier to pronounce. That is why it becomes ýmsar instead of "ýmisar".

Why is the adjective gott in the neuter form if the records (plötur) are feminine?

The adjective gott (good) describes the noun úrvalið (the selection), which is a neuter noun. The sentence is made of two independent clauses joined by og (and); gott agrees with the neuter singular subject in the first half and has no connection to the feminine plural plötur in the second half.

Why does the word for records (plötur) have an ö if the singular is plata?