ASCII art uncompression from a base-n number
05AB1E, 7 6 bytes
gв¹sèJ

Since it was inspired by an 05AB1E answer, an answer given in 05AB1E seems fitting. :)
-1 byte thanks to @Emigna by removing the foreach and doing this implicitly.
Try it online or verify all test cases.
Explanation:

g         # `l`: Take the length of the first (string) input
 в        # And then take the second input in base `l`
          # For each digit `y` of this base-converted number:
  ¹sè     #  Push the `y`'th character of the first input
     J    # Join everything together (and output implicitly)