Step 1 :The graph of the function $f(x)=16^{x}$ is reflected about the $x$-axis and shifted upward 3 units. This means we change the sign of the function and add 3 to it. Therefore, the new function $g(x)$ is $-16^{x} + 3$.
Step 2 :The y-intercept of a function is the value of the function when $x = 0$. So, to find the y-intercept of $g(x)$, we substitute $x = 0$ into the equation of $g(x)$, which gives us $(0, 2)$.
Step 3 :The domain of a function is the set of all possible x-values, and the range is the set of all possible y-values. Since $16^{x}$ is defined for all real numbers, the domain of $g(x)$ is all real numbers. The range of $g(x)$ is all real numbers less than or equal to 3, because the function $-16^{x}$ decreases as $x$ increases, and the function is shifted upward by 3 units.
Step 4 :Final Answer: The equation of the new function, $g(x)$, is \(\boxed{g(x) = -16^{x} + 3}\). The $y$-intercept of $g(x)$ is \(\boxed{(0, 2)}\). The domain of $g(x)$ is \(\boxed{(-\infty, \infty)}\) and the range of $g(x)$ is \(\boxed{(-\infty, 3]}\).