Here are the simplified forms of the given expressions:

1. $b^5 \cdot b^3$ simplifies to $b^8$.
2. $\left(\frac{r^2}{s^4}\right)^3$ simplifies to $\frac{r^6}{s^{12}}$.
3. $(-2)^3$ simplifies to $-8$.
4. $\frac{10m^6}{2m^{10}}$ simplifies to $\frac{5}{m^4}$.
5. $(Cm^3)^5$ simplifies to $C^5m^{15}$.

Would you like any detailed explanations on these steps or have any questions?

Here are some related questions for further exploration:

1. What rules of exponents are used to simplify expressions like $b^5 \cdot b^3$?
2. How do you handle negative bases raised to an odd power?
3. What is the rule for simplifying a fraction raised to a power, such as $\left(\frac{r^2}{s^4}\right)^3$?
4. How do you simplify expressions with variables in the numerator and denominator with different powers?
5. How does distributing an exponent over a product, like $(Cm^3)^5$, affect each term?

Tip: When simplifying exponential expressions, always apply the power and multiplication rules carefully to keep track of exponents!