I found this one I posted awhile back and decided to send it as a submitted snippet, along with some modification to include events needed to reply to backward text. I also include a switch to enable and disable the script.

What this snippet does is basically to respond to people's text, action and notice with a backward output, as well as see yourself enter text backward.

menu * {
  Turn Backward Text $upper($iif($group(#bw) = on,off,on)) {
    $iif($group(#bw) != on,.en,.dis) $+ able #bw
    goto $iif($group(#bw) = on,o,f)
    :o | echo -at * Backward text has been activated! | halt
    :f | echo -at * Backward text has been deactivated! | halt
  }
}
on *:text:*:*:$iif($group(#bw) = on,bw $strip($1-))
on *:action:*:*:$iif($group(#bw) = on,bw $strip($1-))
on *:notice:*:*:$iif($group(#bw) = on,bw $strip($1-))
on *:input:*:$iif($group(#bw) = on,bw $1-)) | .msg # $strip($1-) | haltdef
#bw on
alias -l bw {
  var %x $0 | while (%x >= 1) { 
  var %y %y $ [ $+ [ %x ] ] | dec %x }
  $iif($event = input,echo -bfilt # $+(<,$nick(#,$me).pnick,>),$&
    .msg $iif(#,#,$nick)) %y
}
#bw end