Common Blade generation in XB2

How Common Blade generation works:

1) The game determines which idea to use. If you used a booster, that idea (and its level) is used. Otherwise, the game chooses your single highest idea - and in the case of a tie, chooses one of the highest at random (this works the same as with a rare blade)

2) The game calculates your blade's capacity. This is a value between 1 and 15. This has multiple steps to it:
a) Your level is used to determine a random base capacity between 1 and 10. Levels are grouped in multiples of 10, e.g. level 1-10 has the worst rates, then 11-20 and so on up to 90-99 being the best. To give an idea of these values: Level 1-10 averages 2.865, Level 41-50 averages 4.75, Level 91-99 averages 7.8 and has a minimum of 5. See https://thealexbarney.github.io/xenoblade2-data/bdat/common/BTL_CmnBl_Power.html if you want more info - level ranges on the left, chances are all out of 1000.
b) The crystal you used has a base value attached as well. Common is 0, Rare is 4, Legendary is 8.
c) Your used idea is divided by 5 and rounded down. E.g. at an idea of 10, this gives a value of 2.

d) Finally, all of the above are added together. Your base capacity between 1-10, your crystal value, and your idea bonus, to give a total capacity. 15 is the maximum - if your score would go above 15, the game uses 15.

As a side note: At level 91-99 with a legendary crystal and ideas of 10, you are guaranteed to get the highest capacity possible. This doesn't guarantee that you'll e.g. get 4 crown blades or that they'll be good! It just means you've got the best odds and there's nothing else you can do to improve your chances. Also note that the luck stat has no effect.

3) A Blade Template is chosen. As far as I can tell at this point, it determines the max number of favourite items and favourite categories they can have. Higher idea values open up more possibilities here, and make blades with more favourites more likely. It also determines which field skills the blade can have - Compassion and Justice are more likely to allow only Merc Mission field skills, while Bravery and Truth are more likely to allow only collection field skills.

4) A Blade Attribute (element) is chosen, based on your used idea. Your idea's elements are 7/3 times as likely to be chosen each, or about 2.33x as likely. Or to put that in context, it's about a 24% chance for each of your ideas elements and a little over 10% for each other element. Note that Light can never be chosen, so for Justice the odds are a little different: 28% for Dark and 12% for each other element.

5) A Blade weapon is chosen. If this is Twin Rings, the blade automatically becomes a male animal, otherwise it becomes a humanoid with random gender.

6) The Blade's model is chosen, then their name, then their personality (voice). The gender and if male, whether they're a brute or normal male is the only thing that actually affects the blade. Males have an increased chance to be a brute if your idea values are higher, and brutes get different specials. As far as I can tell everything else is cosmetic stuff, which I'm personally not too fussed about working out the fine details of.

7) The blade's aux core slots, Stat mod type and effectiveness are determined. Aux core slots and how powerful the stat mod are depends on your capacity. At 15 capacity, there's a 60% chance of 3 aux slots and 40% of just two. The stat mod is a random number in a range depending on capacity. At 15 capacity, it's random between 15 and 24. The stat mod type depends solely on the weapon. Full table for the curious: https://thealexbarney.github.io/xenoblade2-data/bdat/common/BTL_CmnBl_StatusType.html (Stats are in order: HP, Strength, Ether, Dexterity, Agility, Luck). Every weapon as a 5% chance for giving luck, and in general they follow about what you'd expect - e.g. Ether Cannons give Ether often (40%), Dexterity a moderate amount (20%) and rarely give Agility or HP (5% each).

8) The blade's armour ratings (Defence & Ether Def) are determined. These are random between a set minimum and maximum for each weapon type, for example a Shield Hammer blade can get between 20-34% Physical Defence and between 20-29% Ether Defence. Capacity has no impact here.

9) The blade's specials are selected. The specials and their effects are determined entirely by the body type and weapon. However, the number of nodes on the affinity chart for each is determined by capacity. At 15 capacity, there's a 60% chance of 5 nodes and a 40% chance of 4 nodes.

10) The blade's level 4 special is selected, and... something to do with its power is determined. If I had to guess, it determines a % multiplier on the special damage. At level 15, this is between 75 and 184.

11) The blade's arts are chosen. First a random number of arts to have is selected between 1 and 3, depending on blade level. At 15 capacity this has a 60% chance to be 3 arts, 40% to be 2 arts. The arts chosen are weighted depending on weapon, for example Chroma Katanas get Critical Up frequently, but Back Attack Up, Nullify Reaction and Arts Plus rarely. Also note that Common Blades cannot get the Draw Aggro Battle Art.

12) A number of battle skills between 1 and 3 is chosen depending on Capacity. As usual, for a 15 capacity blade this is a 460% chance for max (3 skills) and a 40% chance of one less (2 skills). Then for each battle skill, its max level on the affinity chart is determined, for 15 capacity blades it's 60% for 5, 40% for 4 as usual. Note also that your blade role (Hlr/Atk/Tnk) may prevent certain types of skills being selected, for example only Hlr blades can get Healing Wind which recovers HP on switch out.

13) Field skills are chosen a little differently. How many you get is based on driver level, rather than capacity. At level 61 or above, it's MEANT to give a 10% chance of 1, 45% chance of 2 and 45% chance of 3 nodes. However due to a bug, any time you're above level 15 it uses the odds 40% chance of 1, 45% chance of 2 and 15% chance of 3 nodes. Then each one is chosen randomly from the list of skills available to common blades. Bear in mind that there's a chance a given blade won't be able to get mercenary or field skills, depending on its template chosen in step 3. Finally, each of these simply has a random number of levels between 1 and 3. Due to a quirk in how this is randomised, the skills Botany, Earth Mastery, Wind Mastery and Electric Mastery have a 20/20/60 % chance of being levels 1/2/3 respectively, while everything else is 1 in 3 for each level.

14) Favourite categories and items are determined, based on the max count of each from the template chosen in step 3.

15) Finally, the blade's crown rarity is determined! This is based purely on the number of nodes the blade has on their affinity chart. 18 or less is one crown, 19-28 is two crowns, 29-37 is three crowns, 38-44 is four crowns. 44 is the max you can get, which is 5 for affinity keys, 15 for specials, 15 for battle skills and 9 for field skills.

And that's it. The 15 steps the game goes through to generate common blades.