Before you install, understand the significant trade-offs. Using a modified IPA like Watusi violates WhatsApp’s Terms of Service. Here is what can happen:

Finally, the Watusi icon appeared on his home screen. When he opened it, the app looked familiar, yet transformed. He could now hide his "typing" status, keep deleted messages from disappearing, and lock specific chats with a passcode.

This is the most common free method for non-jailbroken devices.