Final answer:
The sentence needs a comma to separate the two clauses.
Step-by-step explanation:
The subject of this question is English. The sentence given is a simple sentence, and it can be corrected by adding a comma to separate the two clauses. The corrected version would be: Roronoa Zoro's dog, which is almost as tall as a horse, always knocks me over when we play fetch.
Learn more about punctuation in English sentences