Answer
See graph.
domain $(-\infty,\infty)$, range $(-\infty,1)$, H.A. $y=1$.
Work Step by Step
Step 1. To obtain the graph of $f(x)=1-2^{x+3}$ from $y=2^x$, shift the curve 1 unit to the left, reflect across the x-axis, then shift 1 unit up. See graph.
Step 2. We can determine the domain $(-\infty,\infty)$, range $(-\infty,1)$, horizontal asymptote H.A. $y=1$.