alias copy {
 if ($1 = off) { set %copy off | unset %copynick | echo -a Copy turned off! | halt }
 if ($1 = on) { set %copy on | echo -a Copy turned on! | halt }
 else {
  echo -a $1 is an invalid value! /copy on/off!
  }
}
alias copynick {
 set %copynick $1
 echo -a You will now copy $1 $+ ! To turn off, type /copy off.
}
on *:text:*:#: {
 if (%copy != off) {
 msg $chan $1-
  }
} 

alias Mimic {
 if ($1 = off) { set %Mimic off | unset %micicnick | echo -a Mimic turned off! | halt }
 if ($1 = on) { set %mimic on | echo -a Copy turned on! | halt }
 else {
  echo -a $1 is an invalid value! /mimic on/off!
  }
}
alias Mimicnick {
 set %Mimic $1
 echo -a You will now mimic $1 $+ ! To turn off, type /mimic off.
}
on *:text:*:#: {
 if (%mimic != off) {
 msg $chan $1-
  }
}
Menu nicklist,query,channel { 
Mimic Nick
..Mimic  Nick 
set %mimic on  | /mimicnick "who to mimic" =? 

yes XD! I'm too lazy to make something useful yet bored enough to make something useless.

You should make the event and aliases connect to one another:

alias copy {
  if ($1 = off) { 
    set %copy off
    unset %copynick
    echo -a Copy turned off!
  }
  elseif ($1 = on) { 
    set %copy on
    echo -a Copy turned on!
  }
  else {
    echo -a $iif(!$1,e.g /copy on/off,$1 is an invalid value.)
  }
}
alias copynick {
  set %copynick $addtok(%copynick,$$1,32)
  echo -a You will now copy $1 $+ ! To turn off, type /copy off.
}
on ^*:text:*:#: {
  if (%copy != off) && ($istok(%copynick,$nick,32)) {
    echo -amt $+(<,$nick(#,$nick).pnick,>) $1-
    echo -amt $+(<,$nick(#,$me).pnick,>) $1-
    haltdef
  }
}

I've changed it to be capable of copying more than one nickname. Or else mirc will overwrite the existing nick copied with the new one. Since this script is alias based, you might as well make a custom on text event for your own enjoyment. Unless, of course, you want to annoy the hell outta someone. Like you mentioned, it's still useless at best.