Answer:
Before the parade, my friend Baby Luigi practiced his baton twirls.
Step-by-step explanation:
An appositive is a noun or noun phrase placed next to another noun in order to explain or identify it. It's usually found after the noun it refers to, although it doesn't have to be. Depending on how essential it is, it can be framed by commas.
When the noun being explained is too general without the appositive, the appositive is considered essential to the meaning of the sentence. In this case, we shouldn't frame it by commas.
This is the case in the given sentence. The phrase Baby Luigi is the appositive that identifies the speaker's friend. If we left out that phrase, the sentence would be too vague.