Video Tutorial :
THIS IS MOST RELIABLE METHOD I'VE FOUND FOR DUPLICATING APPS SO FAR.
You can duplicate / clone any App Store app on iOS 8.0/8.1/8.2/8.3/8.4 by following these simple steps:
1) Open Cydia and add this source: http://apt.25pp.com
2) install these two Packages
as this : http://i.imgur.com/NrXKVaw.jpg
( Green checked packages ) and reboot iPhone if asked.
3) PP application will be on your homescreen. It is a Chinese app so you will have hard time getting things together. I will guide you through screenshots.
4) Open the App, then go to "search" on top bar
5) Search for the app you want to duplicate then download it.
Say for example 'Whatsapp'.
(IMPORTANT NOTE: You should download the App from the 25PP store otherwise the duplicated App won't work)
if you've already installed that app from appstore delete it and reinstall from ppstore
6) Downloading may take long time than usual because of low transfer rates. It's may be because of their server.
7)After downloading it will install app automatically and you will find installed app on your homescreen as usual.
8) Open PP25 app and go to last tab :
Link : http://i.imgur.com/fNpV8Rx.png
9) Choose Duplicate.
10) Now it will show you all the apps that are installed on your iDevice, Choose the App you want to Duplicate (again : you should download the App from the 25PP store otherwise the duplicated App won't work.) and chose Duplicate
11) Chose the duplicated App Name, then tap Duplicate.
screenshot : http://i.imgur.com/Z9rFGNR.png
12) Wait for it to complete, then go to the springboard and you'll find the duplicated app.
P.S : THIS METHOD WORKS WITH ALMOST EVERY APP. I HAVE TRIED WHATSAPP,INSTAGRAM,ALIEN BLUE,TWITTER ETC.