The electro-mechanical parts seem conceptually simple and are mainly a matter of styling and construction. The main issue I see is that the sketch needs some way to receive information from twitter.
The main options I can see are :
- Install an application on the PC to access twitter and send commands to the 'angry bird' via serial over USB (this is the simplest, but requires some software installation on the host PC which makes your product platform-specific). You would need to solve the problem of identifying the right serial port.
- Provide the Arduino with a WiFi or Ethernet interface (and proxy details and credentials etc) and access twitter from the Arduino.
- Provide a 3G modem (and data plan) and access twitter from the Arduino.