- Alternative Character Interpretation: Due to Bel-imperia's aside confession that her initiation of a relationship with Horatio is motivated by her desire to spite Balthazar, it is ambiguous to what extent she genuinely loves Horatio, and to what extent she is just using him as a tool for her vengeance.
- Designated Villain: The Duke of Castile, who is stabbed by Hieronimo and condemned to eternal punishment along with the villains. Yet he's not in league with them and seems to have pretty good intentions, especially when he tries to investigate his son Lorenzo's dishonest obstruction of Hieronimo's attempts to see the king. His worst action is to try to arrange the marriage of his daughter Bel-imperia to Balthazar, whom he likely does not know is a villain.
- Genre Turning Point: This play paved the way for for Elizabethan and Jacobean authors of drama and tragedy such as Christopher Marlowe and William Shakespeare. Kyd introduced the classic revenge plot, Feuding Families in fancy exotic settings, and most importantly the use of iambic pentameter and blank verse to tell a tragedy. The English, rather than feeling like they were playing second fiddle to the tragedies of Spain and Italy, could then have a homegrown version in colloquial language, and this marked the start of the Golden Age of English Literature.
- Moral Event Horizon: The brutal murder of Horatio in Hieronimo's garden is this for Lorenzo, and possibly the other conspirators too.
- Older Than They Think: Numerous important elements of William Shakespeare's Hamlet, such as the ghost calling for revenge, and the use of a play-within-a-play to trap the villains, were inspired by this play. For what it's worth, both works include a guy named Horatio too.
YMMV / The Spanish Tragedy