Rivals of Ixalan is a small set with 70 commons, 60 uncommons, 42 rares, 12 mythic rares, one variation of each standard basic land, and 7 double-faced cards. Not counting the double-faced cards, this is the normal size for a small set of this era. Foil cards are included in booster packs with advertised odds of 1 : 67 cards. The set was printed in English in the USA and Belgium.
Rivals of Ixalan was sold in 15 card booster packs (which contain an additional ad card). Booster boxes have 36 packs.
The US printing uses sequential collation.
Packs are back-facing and have only 10 commons followed by 3 uncommons, a rare, a basic land or checklist, and an ad card. If there is a double-faced card, it will replace the rare and appear after the checklist. Packs with a double-faced card will always contain a checklist instead of a basic land (including double-faced foil cards). If there is a foil, it will displace a common and appear before the basic land or checklist.
|10 Commons||3 Uncommons||1 Rare||1 Land||1 Ad Card|
|10 Commons||3 Uncommons||1 Rare||1 Checklist||1 Ad Card|
|9 Commons||3 Uncommons||1 Rare||1 Foil||1 Land||1 Ad Card|
|9 Commons||3 Uncommons||1 Rare||1 Foil||1 Checklist||1 Ad Card|
|10 Commons||3 Uncommons||1 Checklist||1 DFC||1 Ad Card|
|9 Commons||3 Uncommons||1 Foil||1 Checklist||1 DFC||1 Ad Card|
There are four common runs: A, B, C1, and C2. Half of packs have A, B, and C1 and half have A, B, and C2. Run A has 22 distinct cards each printed three times, and B has 18 cards each printed three times. These are probably on the same sheet. C1 has 16 cards each four times and two copies of Buccaneer's Bravado, and C2 has 13 cards each four times with the other two copies of Buccaneer's Bravado. These are probably also printed together on a sheet.
C1 packs have 3 A cards followed by 2-3 B cards and 4-5 C cards. C2 packs have 3-4 A cards followed by 2-3 B cards and 4 C cards.
When a foil appears in a pack, it will displace a common card. Common foils displace C2 commons. Uncommon foils displace B commons. Double-faced foils displace A commons. Rare foils displace C1 commons and always appear in the same pack as a (non-foil) double-faced card.
The common foil sheet includes copies of the all the basic lands that also have non-foil versions in this set.
The uncommons are split into an A and B run each with 30 distinct cards appearing four times each. Packs have either two A uncommons followed by a B or one A uncommon followed by two B uncommons.
Double-faced cards appear in 1/8 of packs.
The basic lands and checklists are apparently printed on separate sheets. Not counting the checklists that appear with double-faced cards, the rate of checklists is still at least 1/12. (I have seen rare only rare cases that don't fit the 1/12 pattern, so it shouldn't be much higher.) Besides the new Rivals of Ixalan lands, two of the classic Ixalan land variations are available for each land type. These are the two variations with the largest collectors' numbers. All three of these land variations are approximately equally likely.
The A common run consists of 22 different cards each appearing three times. The cards alternate between white, blue, and red. The exception is Fanatical Firebrand which appears once as a card of each color. The choice of first card is mostly arbitrary.
The B common run consists of 18 different cards each appearing three times. There are cards are alternating black and green. The choice of first card is mostly arbitrary.
The C1 common run consists of 16 different cards each appearing four times plus two copies of Buccaneer's Bravado. It includes cards of all colors and colorless cards. The choice of first card is mostly arbitrary.
The C2 common run consists of 13 different cards each appearing four times plus two copies of Buccaneer's Bravado. It includes cards of all colors and colorless cards. The choice of first card is mostly arbitrary.
The A uncommon run consists of 30 different cards each appearing four times. The choice of first card is mostly arbitrary.
The B uncommon run also consists of 30 different cards each appearing four times. The choice of first card is mostly arbitrary.
Most of the marketing cards in Rivals of Ixalan have a token or emblem on the front face. Some of the tokens are duplicates of Ixalan tokens including that expansion symbol, but not all Ixalan tokens appear here. In addition, there is a card that has an advertisement for a Magic-themed Minecraft addon on the front face. (The front has a PEGI rating and the back has ESRB, so I'm not aware of any region differences.) The cards are printed on an 11 × 11 sheet with different items appearing different numbers of times. The choice of first card is mostly arbitrary.
|Elemental × 4||Huatli, Radiant Champion Emblem × 4||Elemental × 6|
|Golem × 6||Treasure × 8||Treasure × 8|
|Treasure × 8||Treasure × 8||Dinosaur × 9|
|Minecraft Ad Card × 10||Saproling × 11||Merfolk × 12|
|Vampire × 12||City's Blessing × 15|
There is a picture of the foil rare sheet available.  In the first 96 slots, each rare card appears twice, and each mythic rare card appears once. Then the sequence repeats. The repeated cards may be fillers or there may be additional complementary sheets. (For this to make sense, I think there would be four sheets with the 96 card sequence repeated five times and four fillers.)
 A picture of the foil US rare sheet was posted in the Misprints facebook group by Tyler Thebeau.