Open Retroarch on your gameshell
Select Load Core
Select Download Core
Select Mr. Boom (Bomberman)
Quit Retroarch
Connect your device to your gameshell with SSH
cd ~/.config/retroarch/cores
(If you use another folder to save your cores go navigate there)
mv mrboom_libretro.so /home/cpi/apps/emulators
nano ~/apps/launcher/Menu/GameShell/Bomberman.sh
(change Bomberman if you want another name in the menu)
Add:
retroarch -L /home/cpi/apps/emulators/mrboom_libretro.so
Save and quit
Move the icon to ~/apps/launcher/skin/default/Menu/GameShell
Make sure the icon has the same name as the .sh file. In this case Bomberman.png
Reboot and have fun :D.