At the top of mob_cmds.c in the command table you want to put this at the
bottom above {"", 0} 

{"advance",  do_mpadvance},

=======*****=======*****========*****========*****=======*****=======
At the very bottom of mob_cmds.c add the following code :

/*************************************************************
*   Used for a mob to advance players!                     *
* Made by Terraco of FSmud and Bojack of DBA      *
* July 25 2009 If you use this be sure to leave this    *
* box of credits. Thank you.                                    *
*************************************************************/
void do_mpadvance( CHAR_DATA *ch, char *argument )
{
    char arg1[ MAX_INPUT_LENGTH ];
    char arg2[ MAX_INPUT_LENGTH ];
    char buf[MAX_STRING_LENGTH];
    CHAR_DATA *victim;
    int level, iLevel;

    argument = one_argument( argument, arg1 );
    argument = one_argument( argument, arg2 );

    if (arg1[0] == '\0' || arg2[0] == '\0' || !is_number(arg2)) {
            bug ("Mpadvance - Bad syntax from vnum %d.", IS_NPC(ch) ? ch->pIndexData->vnum : 0);
            return;
    }

    if ( ( victim = get_char_world (ch, arg1) ) == NULL)
        return;

    if (IS_NPC (victim) )
        return;

    if (victim->desc->original != NULL)
        return;

    if ((level = atoi (arg2)) < 1 || level > MAX_LEVEL)
        return;

    for (iLevel = victim->level; iLevel < level; iLevel++)
    {
        victim->level += 1;
    }
    sprintf (buf, "You are now level %d.\n\r", victim->level);
    send_to_char (buf, victim);
    save_char_obj(victim);

}

=======******=======*******=======******=======******========
At the bottom of mob_cmds.h under mpremove you want to add in:

DECLARE_DO_FUN( do_mpadvance    );