The Fantasmic dining package is a great perk for eating at selected restaurants at Hollywood Studios. The package includes reserved seating in the Fantasmic amphitheater (the best seats in the house). This does not mean you get a specific seat, but the center seating section of the amphitheater is reserved for guests who purchase the dining package, and those seats fill at a first come first serve basis.
The Fantasmic dining package is available at these Hollywood Studios restaurants:
Hollywood Brown Derby (2 table service credits)
Mama Melrose (1 table service credit)
Hollywood & Vine (1 table service credit)
Quite frustratingly, The Fantasmic dining package usually is bookable within 150-170 days before the day you want to eat, not the usual 180. That's due to the packages being put online on a month-by-month basis, not exactly 180 days like regular restaurant bookings. You usually find that towards the end of the current month the whole 6th month ahead will become available. (For example, about the last week of March, September's will be made available).
Top Tip: We always book to eat at Hollywood and Vine and always take advantage of the Fantasmic dining package. At 180 days, we usually book Hollywood & Vine the normal way just to make sure we get our reservation in. Then within the month after, I keep an eye on the dining package page and overwrite the reservation with the Hollywood & Vine Fantasmic package when it's made available. You have to be quick though, the Fantasmic dining package do sell out quickly.
For Disney Dining plan guests, it costs no extra! You pay the same dining plan credit as you would eating at one of the restaurants normally. If you're not using the dining plan and paying with cash, there is sometimes an extra cost–around $5 per person–added onto the meal price for this package.
When you're having your meal, at some point your server will bring over the Fantasmic vouchers. About half an hour before show time, head over to the amphitheater (which is just before Tower Of Terror), and head on through the Fastpass+ queue. Keep in mind, sometimes there might be two showings of Fantasmic. If there is, your voucher will most probably be for the first showing.
If the show is cancelled for any reason (the main reason being weather), you can use the voucher at any night up to a week after. If you're unable to return, go to guest services and they might do something for you.
The only real downside to the Fantasmic dining package is you have to eat quite early. The latest you can usually book a table for is 5pm.
Some people do get confused and just book a regular Hollywood & Vine reservation thinking they'll get the voucher, but they will not. You must book the dining package through the dedicated Fantasmic package page here.
If you're using the Disney Dining plan, then getting the Fantasmic package is no a brainer if you're going to watch the show (and you really should every chance you get).