This code creates a scatter plot of horsepower vs. mpg using the `relplot` function from Seaborn. The `kind="scatter"` argument specifies that we want a scatter plot, and the `size="cylinders"` argument sets the size of each point based on the number of cylinders in the car.
```python
# Import Matplotlib and Seaborn
import matplotlib.pyplot as plt
import seaborn as sns
# Create scatter plot of horsepower vs. mpg
sns.relplot(x="horsepower", y="mpg",
data=mpg, kind="scatter",
size="cylinders")
# Show plot
plt.show()
```
Note that `mpg` is assumed to be a pandas DataFrame containing the relevant data. If you haven't already loaded the data into a DataFrame, you'll need to do that first using something like:
```python
import pandas