1. The problem is to simplify the expression $Y^4 - 8z$. 2. This expression consists of two terms: $Y^4$ and $-8z$. 3. Since these terms involve different variables and powers, they cannot be combined or factored further. 4. Therefore, the simplified form of the expression is simply $Y^4 - 8z$. 5. No further simplification or factorization is possible because the terms are unlike terms. Final answer: $Y^4 - 8z$