Learn Danish: Hvis pigen bærer korset, forsvinder det onde spøgelse. - If the girl carries the cross, the evil ghost disappears.

This is because of the V2 (verb-second) rule. The entire "if" clause (Hvis pigen bærer korset) counts as the first piece of information in the sentence. To keep the main verb in the second position, the main clause must start with the verb (forsvinder) followed by its subject (det onde spøgelse).

Why doesn't the V2 rule flip the subject and verb in the first part of the sentence (Hvis pigen bærer korset)?

Subordinate clauses (clauses that start with words like hvis, at, or fordi) have a fixed word order: conjunction + subject + verb. The V2 rule only forces the verb into the second position in main clauses, which is why the flip only happens after the comma.

Why is it det onde spøgelse instead of det ond spøgelse?

When you use a definite article like det (the) with an adjective, the adjective needs an -e at the end. Even though spøgelse is a neuter word, the adjective ond (evil) becomes onde in this definite phrase.

How do we know the gender of the word for "cross" from this sentence?

You can tell it is a neuter word (an et word) because it ends in -et in its definite form: korset (the cross). If it were an en word, it would end in -en.