Learn Polish: Ja bym nigdy nie chciał być niewidzialny.

This showcases the mobility of the conditional particle by. While you can perfectly well say Ja nigdy nie chciałbym, Polish allows you to detach by (and its personal ending -m) and attach it to the first stressed word in the sentence. Doing this often adds a slight conversational emphasis to that first word.

Since Polish usually drops subject pronouns, why is Ja included here?

Pronouns are kept for emphasis or contrast, meaning I would never want this, even if someone else might. Placing Ja at the start also provides a strong anchor for the mobile particle bym. If you dropped the pronoun, the particle would shift to the new first word, making it Nigdy bym nie chciał być niewidzialny.

Why does the sentence use both nigdy and nie?

This is a reminder about Polish double negation. Whenever you use a negative word like nigdy (never), nigdzie (nowhere), or nikt (no one), you must also negate the main verb with nie. A literal translation would be 'I would never not want'.

After the verb być (to be), shouldn't the following word be in the instrumental case? Why is niewidzialny in the nominative?