Giygas ( Battle )
Now with the Devil's Machine off, you will focus directly on Giygas.
Don't try Multi Bottle Rockets anymore, they won't work. Use Jeff's Heavy Bazooka instead if you have it.
Ness use PSI Rockin, Paula use PSI Freeze and Poo use Starstorm.
Giygas will unleash bizarre attacks that can cause all kind of status ailments and even death. Keep healing your party as needed. Eventually Pokey will return.
Third and Final Form
Pokey tells you to call for help if you can. Which gives us a hint as to how to handle the third form. Paula has telepathy and can communicate over great distances.
For this form, make sure Paula uses Pray every time.
Everyone else can focus on healing and making sure Paula does not die.