LE version

tl;dr

• New strengths and weaknesses for each playable race that impact how you play
• Effects are meaningful for NPCs, changing how you engage them in combat
• Conditional passives instead of powers
• Players can choose whatever effects they want regardless of their race
• Ludicrously compatible (even with other race overhauls!)
  

Legacy overhauls the racial effects of the playable races, taking them from boring, imbalanced and forgettable to diverse, challenging and meaningful. Here's a high level summary:

• Racial effects impact NPCs too. Vanilla races and most race overhauls focus on the experience of playing as a race, as opposed to the experience of playing against a race. So races get daily powers only the player uses (e.g. Beserk), passives that mean nothing to NPCs (e.g. Imperial Luck), or effects that due to engine limitations only work on the player (e.g. Natural talent from Aetherius). In Legacy, racial effects affect player and NPC alike. This adds a new layer of strategy as tactics that work for or against a Nord might not work so well for or against an Argonian.
• Racial effects come with costs as well as benefits. All race overhauls give unique benefits to each race, but past elder scrolls games traded these off against weaknesses. Legacy reinstates this tradition. Because these drawbacks are meaningful to NPCs too this allows you play to your enemy's weaknesses, further rewarding strategic play.
• No powers, conditional passives instead. Daily powers have two problems: (1) NPCs don't use them, and (2) the player is tempted to save them indefinitely for imagined future fights. As a result they end up forgotten. Legacy fixes this by replacing powers with conditional passives. They activate whenever conditions are right, and apply to NPCs as well as the player. You'll now face off against Beserk orcs and dark elves consumed by Ancestral Wrath. These effects activate as often as the conditions are met so there's no need to save powers for the right moment. Legacy leaves the vanilla daily powers in place though, just in case players really like them.
• Total freedom for the player. All racial effects reward certain playstyles. In the extreme this can force races to play a certain way, which harms replayability. To avoid this Legacy prompts the player to choose their racial effects through a pop-up menu, regardless of their actual race. You can change them at any time through the MCM, and even pick multiple racial effects. So, whether you want to be a "pure-blooded" Nord, an Imperial with High Elf ancestry, or a Wood Elf raised by Orcs, the choice is yours!
• Balance. Racial effects can intuitively overpower the player, but because they apply to NPCs too they can also imbalance the game. The best example of this is vanilla's 50% frost resist for Nords. While lore friendly, it makes it virtually impossible to be a frost mage because Nords are everywhere in Skyrim. Legacy is designed with an eye on player power and NPC balance.
  

Note that the player can choose their racial abilities separate from their actual race, and you can even choose multiple racial effects. When installing or starting a new game you a pop-up menu will prompt you to make a choice, but you can use the MCM to edit your choice at any time.

Argonians
Poison affinity: Resist poison, 50%. Poisons are 25% more powerful, but potions are half as effective.
Altered metabolism: All stats regenerate twice as fast, thrice as fast when in water, but also drain quickly. Waterbreathing.


Bretons
Focussed: Enchantments, alteration spells and conjuration spells are 25% more effective. All spells and enchantments are 25% less effective when magicka < 25%, 50% when < 10%.
Defensive: Resist magic, 25%. Mage armor spells increase worn armor rating by 25%. Destruction spells cost 40% more


Dark Elves
Fire affinity: Resist fire, 50%. Frost weakness, 50%. Fire spells are 25% more effective, frost and shock spells are 25% less effective.
Ancestors' wrath: Spells and weapons are 20% more effective when < 50% health, but you are illuminated preventing hiding and/or sneaking.


High Elves
Masters of the arcane: Spells cost 20% less and are 25% more powerful when the target has <50 magicka remaining.
Magical sensitivity: Weakness to magic, 25%
Physically weak: Deal 20% less damage with, and take 20% more damage from, blunt weapons. Enemy armor is 25% more effective


Imperials
Healers: Restoration spells, and potions are 25% more effective.
Regimented: Damage taken is reduced by 25% when blocking, but increased by 25% when not. Deal 20% less damage with, and take 20% more damage from, bows.



Khajiit
Stealthy: Sneak attack multiplier increased by 20%. Move 20% faster.
Muddled: Weak to magic, 15%. Magicka regeneration is halved.


Nords
Savage blows: Power attacks cost 25% less stamina and ignore 50% of enemy armor when stamina > 50%. Move 20% slower and take 20% extra damage when stamina is below 25%.
Honor through bravery: Sneak attack multiplier is halved. Blocking is 25% less effective


Orcs
All or nothing: Take 50% less and deal 50% more damage below 33% health. All regen is reduced by 50% when you have > 67% health.
You puny weakling! Take half damage from, and deal half damage with, daggers. Power attacks deal 25% extra damage to dagger wielding enemies


Redguards
Curved swords: Deal 20% more damage with, and take 20% less damage from, swords.
Tough physiology: Resist poison, 50%.
Fear of daedra: Take 20% more damage from, and deal 20% less damage to, daedra, summons and the undead. Conjuration is 50% less effective.


Wood Elves
Expert archers: Deal 20% more damage with, and take 20% less damage from, bows. Arrows ignore 50% of enemy armor when hitting from the back
Affinity with nature: Take 50% less damage from predators. Resist disease 50%
Small frames: Deal 20% less damage with, and take 20% more damage from, two-handed weapons

Requirements
SKSE + SkyUI. The MCM is how you change your racial effects.
SPID to distribute the effects to NPCs

Installation
Install through your mod manager of choice. When you start a new game a pop-up menu will prompt you to choose your ancestry, though you can change this at any time through the MCM. There's an optional patch to disable the popup for VR users.

Uninstallation
Uninstalling mods mid-playthrough is always a risk because so much stuff gets baked into your save. That said, Legacy should be pretty safe to uninstall. Just make a back-up save first incase things go wrong then go to a cell without NPCs, use the MCM to remove any racial effects from your character, save, exit, uninstall, load. If you know what you are doing it is safer to use xEdit to delete all the records from within the esps rather than disable the esps in your mod manager. This is because changing your load order (e.g. by removing an esp) mid-playthrough can cause problems.

Compatibility
Legacy is bizarrely compatible and you won't get many conflicts unless you run it alongside another race overhaul. Even then, it's actually compatible with other race overhauls as long as you load Legacy first. So you can run it alongside Imperious, Morningstar or Aetherius if you want. Just let those mods overwrite Legacy and you'll get the effects of both. The kinds of conflicts that can arise are:

- Legacy edits the load screens that display information about the playable races. Other race mods probably do the same and which ever loads last will "win".
- Legacy edits the race records for the playable races to change the flavor text shown in the character creation menu. This will conflict with any other mod that edits the race records, but unless you really care about the flavor text you should let other mods overwrite Legacy as there are more important things than flavor text.
- Legacy removes all effects from the vanilla racial abilities. Other race overhauls also modify these abilities (typically replacing their effects with new ones) and you should let them overwrite Legacy.

Performance impact
None. The racial effects rely exclusively on standard perk functions and ability spells. The only script manages the MCM.

Synergistic mods
Skyrim encourages character specialization. Legacy lets your character specialize even further. To add some risk to this process it helps to add mods that penalize specialization, like Know Your Enemy which gives enemies a wider variety of resistances and weaknesses such that no single weapon or spell can get you though the whole game. Curse of the Firmament takes a similar approach to Legacy but edits the standing stones, with the two together you can build some highly specialized characters.




My Other Mods

Building Your Character - diverse and fun builds with strengths and weaknesses
Master of One - A perk overhaul that transforms perks from generic character progression into a means to craft unique and specialized builds.
Curse of the Firmament - A standing stones overhaul that emphasizes tough choices.
Legacy - A race overhaul that bring strengths and weaknesses to each race.
Acolyte - A progressive-yet-unobtrusive religion overhaul with a long path to divinity.

Enemies and Combat - challenging, varied and fair combat
Know Your Enemy (armor module, patcher version) - A resistance and weakness overhaul for enemies and armors.
Know Your Enemy 2 (armor module, integration patch) - An upgraded resistance overhaul: more damage types, more configuration, more polish.
NPC Stat Rescaler - A patcher that adjusts player and NPC stats for faster, fairer, and less spongy combat.
Enemy Releveler - A patcher that adjusts NPC levels to truly delevel the world.

Stats and stat growth - drawing out character growth to stave off premature godhood
Exhaustion - Incremental Fatigue - An ultra-lightweight injury/fatigue system.
Exercise - Incremental Growth - An add-on for Exhaustion that converts fatigue into stat growth.
Geometric Stat Growth - Stats grow by a configurable percentage on level up, instead of a fixed value.

Miscellanea
Challenging Spell Learning - Spell Tomes trigger a costly ritual you must pass to learn spells.
Trainers Galore - An expansion of the training system designed for "training only" leveling.
Pick Your Poison - An alchemical handbook to support strategic foraging.
Configurable Perks Per Level - An MCM to edit how many perk points you get on level up.
XP Editor - A patcher that adjusts xp gain and leveling.
Sightseer - Standing Stones - Guidebooks for the standing stones, collectibles to find, and a hidden quest to unite them.

Mod Lists
Thoughtful Skyrim - A small, gameplay-focussed modlist that rewards preparation and planning.

Acknowledgements

Thanks to r/skyrimmods for feedback on mod design. Thanks to the creators of xEdit and zEdit without whom this mod, and particularly the now-retired patcher, would not be possible. Thanks to u/neckedcobra for the image used in the mod page. Thanks to lilmetal for the original Spell Perk Item Distributor ini file and the custom race compatibility patch.