Do we get a $20 ticket with a platinum pass

Sure

Yes

They have mentioned special discounts, but not sure what the discounts for a friend are

Looks like it up to 4 friends.

Can we purchase a $20 ticket for a friend with our platinum pass?

Platinum Pass Includes Unlimited Visits to Cedar Point and Cedar Point Shores Waterpark every public operating day in 2019, Free Parking, Special Discounts, Early Ride Times, Exclusive Ride Nights, and more for less than the cost of three visits! Just 3 Easy Payments of $53* *After initial payment of $61 due today. I hope that this helps you.