Let's begin with what you can expect from each of the three booster types I listed above.
Draft Booster
Number of Cards: 15 and 1 ad card/token card
Number of Versions: 1
Contents:
1 rare/mythic rare
3 uncommons
10 commons
1 land
1 ad card/token card
The booster contents are as you would expect. The Draft Booster has the possibility of containing borderless planeswalkers or showcase cards. In Throne of Eldraine specifically, there are no non-foil common showcase cards in booster packs. Those appear only in the Collector Booster.
Theme Booster
Number of Cards: 35 cards and 1 reference card
Number of Versions: Varies (Throne of Eldraine has 5, one of each color)
Contents:
1.1 rares/mythic rares
33–34 commons/uncommons
1 reference card
Nine out of ten Theme Boosters will have one rare, but one out of ten will have two rares. That's what "1.1 rares" means. The number of commons and uncommons in theme boosters varies between boosters, unlike Draft Boosters where the number of each rarity mostly remains constant. You'll always get more commons than uncommons, however. The reference card is new-player information on a card to help expose newer players to different aspects of the game.
Collector Booster
Number of Cards: 15 cards and 1 foil token card
Number of Versions: 1
Contents:
1 rare/mythic rare with extended art
1 foil rare/mythic rare
9 foil commons/uncommons
3 special-frame cards (showcase or borderless planeswalkers)
1 ancillary card
1 foil token
This booster is a little more complex, so I'm going to walk through each slot:
1 Rare/Mythic Rare with Extended Art
This slot is a rare or mythic rare with extended art. Every rare or mythic rare from the set that doesn't already have a variant frame (meaning that it doesn't exist as a borderless planeswalker card or showcase card) will be available as extended-art cards. The extended-art cards are all rares and mythic rares and are only found in the Collector Booster.
1 Foil Rare/Mythic Rare
This slot is a foil of any rare or mythic rare from the set, including variant versions such as borderless planeswalker, extended-art, or showcase cards.
9 Foil Commons/Uncommons
These slots are for foils of any common or uncommon from the set, including variant versions such as showcase cards. (Commons and uncommons don't have borderless planeswalker or extended-art cards.)
3 Special-Frame Cards (Borderless Planeswalkers or Showcase Cards)
These three slots will be non-foil variant cards, but not extended art. They'll be borderless planeswalker or showcase cards. These cards will all be non-foil. For Throne of Eldraine specifically, the non-foil common showcase cards will only be found in the Collector Boosters in one of these slots.
1 Ancillary Card (Non-foil)
This slot is for new cards that are connected to the set but don't appear in Draft Boosters. The card pool for this slot can vary from set to set. For Throne of Eldraine, this will be the Buy-a-Box card, the new cards from the Planeswalker Decks, and the new cards from the Brawl Decks (more on this in a moment). This slot is going to be the catch-all for mechanically unique cards associated with the set, allowing collectors to get them here without having to purchase other products or participate in other promotions. These cards will be in non-foil.
1 Foil Token
This slot is a foil version of a token card found in the Draft Booster. The Collector Booster is the only place these token cards will appear in foil in boosters. Note that this slot is only tokens and not any other type of card, such as emblems, that also shows up in the token slot in Draft Boosters.
Those aren't all the products that are going to be associated with Throne of Eldraine, though. Let me walk you through some more.
