The ASCII character countdown!
2sable, 36 bytes
//9#999999//,#,#,221'/,#q',#q,qq2///

\$y=8\$. Used so far: 1'2q#,9/
Try it online.
Maybe this opens up some other languages that use // to comment. :)
Explanation:

2sable is an old version of 05AB1E (legacy) (which of itself is an old version of 05AB1E).
The legacy version outputs a leading newline however: try it online.
And the latest 05AB1E version outputs three leading newline: try it online.
//                                    # Divide twice, no-ops with an empty stack
  9                                   # Push 9
   #                                  # Pop and split it by spaces
                                      # (since it contains no spaces, it only pops)
    999999                            # Push 999999
          /                           # Divide the empty stack by this, popping the integer
           /                          # No-op divide again with an empty stack
            ,                         # No-op print (which would output a newline in the
                                      # newer versions)
             #,#,                     # Some more no-ops
                 221                  # Push 221
                    '/               '# Push &quot;/&quot;
                      ,               # Pop and print this &quot;/&quot; to STDOUT
                       #              # Split the 221 on spaces, so it just pops
                        q             # Exit the program
                         ',#q,qq2/// '# No-ops