Once you've created a Google Spreadsheet with "List Growth" and "Campaign Analysis" sheets, add this script filling your mailchimp API_KEY and LIST_ID

mailchimp-campaigns.gs

/********************************************************************************
 *
 * Mailchimp API - Get Campaign Data into Google Sheets
 * By Ben Collins 2017
 * http://www.benlcollins.com/
 *
 */

var API_KEY = 'MAILCHIMP_API_KEY';
var LIST_ID = 'MAILCHIMP_LIST_ID';


/********************************************************************************
 * call the Mailchimip API to get campaign data
 * This gets all campaigns in an account
 */
function mailchimpCampaign() {
  
  // URL and params for the Mailchimp API
  var root = 'https://us15.api.mailchimp.com/3.0/';
  var endpoint = 'campaigns?count=500';
  
  // parameters for url fetch
  var params = {
    'method': 'GET',
    'muteHttpExceptions': true,
    'headers': {
      'Authorization': 'apikey ' + API_KEY
    }
  };
  
  try {
    // call the Mailchimp API
    var response = UrlFetchApp.fetch(root+endpoint, params);
    var data = response.getContentText();
    var json = JSON.parse(data);
    
    // get just campaign data
    var campaigns = json['campaigns'];
    
    // blank array to hold the campaign data for Sheet
    var campaignData = [];
  
    // Add the campaign data to the array
    for (var i = 0; i < campaigns.length; i++) {
      
      // put the campaign data into a double array for Google Sheets
      if (campaigns[i]["emails_sent"] != 0) {
        campaignData.push([
          i,
          campaigns[i]["send_time"].substr(0,10),
          campaigns[i]["settings"]["title"],
          campaigns[i]["settings"]["subject_line"],
          campaigns[i]["recipients"]["recipient_count"],
          campaigns[i]["emails_sent"],
          (campaigns[i]["report_summary"]) ? campaigns[i]["report_summary"]["unique_opens"] : 0,  
          (campaigns[i]["report_summary"]) ? campaigns[i]["report_summary"]["subscriber_clicks"] : 0
        ]);
      }
      else {
        campaignData.push([
          i,
          "Not sent",
          campaigns[i]["settings"]["title"],
          campaigns[i]["settings"]["subject_line"],
          campaigns[i]["recipients"]["recipient_count"],
          campaigns[i]["emails_sent"],
          "N/a",
          "N/a"
        ]);
      }
    }
    
    // Log the campaignData array
    Logger.log(campaignData);
    
    // select the campaign output sheet
    var ss = SpreadsheetApp.getActiveSpreadsheet();
    var sheet = ss.getSheetByName('Campaign Analysis');
    
    // calculate the number of rows and columns needed
    var numRows = campaignData.length;
    var numCols = campaignData[0].length;
    
    // output the numbers to the sheet
    sheet.getRange(4,1,numRows,numCols).setValues(campaignData);
    
    // adds formulas to calculate open rate and click rate
    for (var i = 0; i < numRows; i++) {
      sheet.getRange(4+i,9).setFormulaR1C1('=iferror(G4/F4*100,"N/a")');
      sheet.getRange(4+i,10).setFormulaR1C1('=iferror(R[0]C[-2]/R[0]C[-4]*100,"N/a")');
    }
    
  }
  catch (error) {
    // deal with any errors
    Logger.log(error);
  };
  
}


/********************************************************************************
 * 
 * Retrives MailChimp list growth data and populates a Google Sheet
 * 
 */
function mailchimpListGrowth() {
  
  // URL and params for the Mailchimp API
  var root = 'https://us15.api.mailchimp.com/3.0/';
  var endpoint = 'lists/' + LIST_ID + '/growth-history?count=100';
  
  var params = {
    'method': 'GET',
    'muteHttpExceptions': true,
    'headers': {
      'Authorization': 'apikey ' + API_KEY
    }
  };
  
  try {
    // call the Mailchimp API
    var response = UrlFetchApp.fetch(root+endpoint, params);
    var data = response.getContentText();
    var json = JSON.parse(data);
    
    // get just list history data
    var listGrowth = json['history'];
    
    // blank array to hold the list growth data for Sheet
    var monthlyGrowth = [];
    
    // Add the list growth data to the array
    listGrowth.forEach(function(el) {
      monthlyGrowth.push([el.month, el.existing, el.optins, el.imports]);
    });
    
    // Log the monthlyGrowth array
    Logger.log(monthlyGrowth);
    
    // select the list growth output sheet
    var ss = SpreadsheetApp.getActiveSpreadsheet();
    var sheet = ss.getSheetByName('List Growth');
    
    // calculate the number of rows and columns needed
    var numRows = monthlyGrowth.length;
    var numCols = monthlyGrowth[0].length;
    
    // output the numbers to the sheet
    sheet.getRange(4,1,numRows,numCols).setValues(monthlyGrowth.reverse());
    
    // adds formulas for absolute and relative growth
    for (var i = 0; i < numRows; i++) {
      sheet.getRange(4+i,5).setFormulaR1C1('=iferror(R[0]C[-3] - R[-1]C[-3],0)');  // absolute monthly change in list
      sheet.getRange(4+i,6).setFormulaR1C1('=iferror((R[0]C[-4] - R[-1]C[-4])/R[-1]C[-4],0)').setNumberFormat("0.00%");  // rate of change in list
    }
    
  }
  catch (error) {
    // deal with any errors
    Logger.log(error);
  };
  
}

Hello, there is a problem with "lenght" I think
TypeError: Cannot read property 'length' of undefined
Thanks

Sorry, this code is two years old and without proper error handling.