i dont know what 'the mana world' is.
but you would need to make a 'the mana world.desktop' file, and an icon
.desktop file would probs need to look like:

[Desktop Entry]
Encoding=UTF-8
Name= (name of app)
Comment= (comment about app)
Exec=/home/user/ (location and name of app)
Icon= (the name of icon)
Terminal=false
Type=Application
Categories=GNOME;Application;Game;

or something like that, but i know nothing about linux, maybe the linux junkies could advise better