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!)
  

Summary

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 lets the player choose their racial effects through an MCM, regardless of their actual race, you can 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.
  

Races

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 should use the MCM to choose your effects.

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 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

Technical information
Requirements
SKSE + SkyUI. The MCM is how you choose racial effects for the player.

Installation
The racial effects of Legacy need to be distributed as a hidden perk to hundreds of NPC records. Legacy includes two ways to distribute the perk without compatibility problems: a zEdit patcher and a Spell Perk Item Distributor ini file. If you use Spell Perk Item Distributor then you can just install the mod the usual way and everything will just work. The zEdit patcher is more involved, and open the spoiler below for instructions. If you use neither then only the player, and not NPCs, will get the new effects.




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 (the base esp, not the patch) 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.



Acknowledgements

tjhm4 for the original SE version
Thanks to r/skyrimmods for feedback on mod design. Thanks to the creators of xEdit and zEdit without whom this mod, and particularly the patcher, would not be possible. Thanks to u/neckedcobra for the image used in the mod page. Thanks to lilmetal for the Spell Perk Item Distributor ini file and the custom race compatibility patch.