The following installation guide describes how to properly install Ygopro on Mac OS X. Click on the images to view a bigger version.
OS X 10.8 or higher.
First download the dmg installer from the download page. Open the dmg by double clicking on it. Mac will mount a disk to your system that is labeled "Install Ygopro Percy".
A small window with 2 icons appears. Drag the icon that says "Ygopro" into the "Applications" icon.
Note: do not start Ygopro directly at this step! The dmg file is read-only. You will not be able to save decks and settings this way.
The installer will now copy the necessary files. This might take a few minutes.
After completing the installation you can eject the image.
To start the game click on "Applications" in the dock, then on "Ygopro". This will open a new page because Ygopro is installed into a folder.
Click on the Ygopro duel disk icon to start.
The app is from an unidentified developer
If the app refuses to start with the message "The app is from an unidentified developer", then follow these steps.
The app will be stored as an exception to your security settings, and you will be able to open it in the future by double-clicking it.
An extra command has been added to solve this problem. Press ctrl+click to cancel moves.
Collect the error report via Report -> Show details. There will be a large screen of text with the error report. Copy that report and post a message on the forum.