Mirrodin Besieged is a small set with 60 commons, 40 uncommons, 35 rares, 10 mythic rares, and two variations of each standard basic land. Besides the lands, 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.
Mirrodin Besieged was sold in 15 card booster packs (which contain an additional ad card). Booster boxes have 36 packs.
There are also prerelease boxes that contain 18 "Mirran Faction" packs containing only Mirran cards and 18 "Phyrexian Faction" packs containing only Phyrexian cards.
The US printing uses sequential collation. Collation is non-standard to support separated Mirran and Phyrexian print runs.
Packs are back-facing and have 10 commons followed by 3 uncommons, a rare, an ad card, and a basic land. If there is a foil card, it will appear after the land, displacing a common.
|10 Commons||3 Uncommons||1 Rare||1 Ad Card||1 Land|
|10 Commons||3 Uncommons||1 Rare||1 Ad Card||1 Land||1 Foil|
The commons are printed on two sheets. One sheet forms the A run with each of the 30 Mirran commons appearing four times, and the other forms the B run with each of the 30 Phyrexian commons appearing four times. Packs contain 5 A commons followed by 5 B commons. A foil can displace a common from either run.
The uncommons are also printed on two sheets, each of which is divided into two runs. The A and B runs contain Mirran cards and the C and D runs contain Phyrexian cards. The A and C runs each have 11 cards each appearing six times, and the B and D runs each have 9 cards each appearing six times. Packs contain one card from three runs (in alphabetic order of run names). Assuming all uncommons appear with equal frenquency, each of A and C should be left out 7/40 of the time, and each of B and D should be left out 13/40 of the time.
The rares are printed on two sheets as well. Again, there is a Mirran sheet (A), and a Phyrexian sheet (B). Tezzeret, Agent of Bolas (the only card besides the basic lands not to have a Mirran or Phyrexian watermark) appears on both sheets. The Mirran sheet has 18 rares and 4 mythic rares. Each mythic rare appears three times and each rare appears 6 times except for Victory's Herald which only appears 5 times (and is thus short-printed). There is additionally one copy of Tezzeret. (This accounts for 120 slots on the sheet.) The Phyrexian sheet has 17 rares and 5 mythic rares. Each mythic rare appears three times and each rare appears 6 times except for Psychosis Crawler which appears 7 times (and is thus over-printed). There are additionally two copies of Tezzeret (for a total of three copies across the two sheets). (This also accounts for 120 slots on the sheet.)
Earlier sources conflict as to the exact make-ups of the rare sheets (and the configuration I have presented is also different). The original map from JustMe and the map published by Ross Edwards (based on JustMe's map) have the sixth copy of Victory's Herald on the Mirran sheet. JustMe's map agrees with mine as to the make-up of the Phyrexian Sheet, but Ross Edwards adds a copy of Phyrexian Rebirth so that it is also over-printed; but this means both sheets now use 121 slots whereas JustMe's are imbalanced. (My sheets are also balanced, and though I think there is some motivation for the sheets being balanced, it is not a completely safe assumption.) In any case, I can't account for the cards added by either map.
Besides the two variations of each basic land with the Mirrodin Besieged expansion symbol, there are also two Scars of Mirrodin variations for each land that can appear in Mirrodin Besieged boosters; these are Plains (232), Plains (233), Island (235), Island (236), Swamp (240), Swamp (241), Mountain (242), Mountain (243), Forest (248), and Forest (249). Because of repetition of the land sheet, it is hard to confirm the full sheet layout, but probably most variations appear six times, and there is one card, probably Scars of Mirrodin Plains (233), that appears seven times. However, there is an error on the sheet where most copies of Mirrodin Besieged Island (148) are replaced with Scars of Mirrodin Island (235). Probably, Mirrodin Besieged Island (148) only appears once on the sheet. (However, note that this Island isn't rare in practice as it also appears in New Phyrexia boosters where it is not short-printed.)
Prerelease faction packs use the same print runs. A faction pack will contain 10 commons from the matching common run. Then, it will have 3 uncommons made up of 2+1 or 1+2 from A and B or C and D as appropriate for the given faction. Then, it will contain a rare from the faction's sheet. Ad cards and lands are the same as for normal packs. I believe foils are also the same as normal packs (meaning that Phyrexian foils may appear in Mirran packs and vice versa).
The A common run consists of 30 different Mirran cards each appearing four times. The choice of first card is mostly arbitrary.
The B common run consists of 30 different Phyrexian cards each appearing four times. The choice of first card is mostly arbitrary.
The A uncommon run consists of 11 different Mirran cards each appearing six times. The choice of first card is mostly arbitrary.
The B uncommon run consists of 9 different Mirran cards each appearing six times. The choice of first card is mostly arbitrary.
The C uncommon run consists of 11 different Phyrexian cards each appearing six times. The choice of first card is mostly arbitrary.
The D uncommon run consists of 9 different Phyrexian cards each appearing six times. The choice of first card is mostly arbitrary.
The A rare run contains 18 Mirran rares each printed six times except for Victory's Herald which is printed five times, and 4 Mirran mythic rares each printed three times, plus one copy of Tezzeret, Agent of Bolas. The choice of first card is mostly arbitrary.
The B rare run contains 17 Phyrexian rares each printed six times except for Psychosis Crawler which is printed seven times, and 5 Phyrexian mythic rares each printed three times, plus two copies of Tezzeret, Agent of Bolas. The choice of first card is mostly arbitrary.
It is hard to confirm the land run because the pattern repeats over the sheet, but I think this run is probably correct. Each land appears six times except for Scars of Mirrodin Plains (233) which appears seven times, and Mirrodin Besieged Island (148) which appears only once with the other places in the pattern where it would appear replaced by Island (235) (which thus appears 11 times). The choice of first card is to put the extra Plains in the last slot (which is consistent with at least one observed transposition).
Most of the marketing cards in this set have a token or tip on the front face. They are printed on an 11 × 11 sheet with different items appearing different numbers of times. The choice of first card is mostly arbitrary. Some of the tokens are from Scars of Mirrodin, printed with the expansion symbol of that set, but not all of those tokens appear here.
|Horror × 1||Golem × 2||Cat × 4|
|Soldier × 4||Thopter × 4||Metalcraft and Imprint Tip Card × 6|
|Proliferate Tip Card × 6||Zombie × 6||Infect Tip Card × 7|
|Living Weapon Tip Card × 7||Battle Cry Tip Card × 9||Myr × 15|
|Germ × 25||Poison Counter × 25|
 The common runs for US Mirrodin Besieged were originally posted by Medussa on the MTG Salvation forums. (A have chosen different starting points for the runs, and chosen to resolve a few transpositions differently in the Phyrexian run.)
 The rare runs for US Mirrodin Besieged were originally posted by JustMe on the MTG Salvations forums. The posts by JustMe no longer exist, but the results are still available, e.g. here. (My take on the runs is a bit different as noted above.)
 The rare runs for US Mirrodin Besieged were also posted by Ross Edwards as a "digital module" supplementing the Black Book series. (This take on the runs is a bit different from mine or JustMe's as noted above.)