Radiant Features

Sleep Feature

Considering she's already become your friend and you've also romanced her, you can ask Serana to sleep in any bed that is player-owned/unowned, considering there's a double bed nearby. Even vampires need some shut-eye every now and then.

When you tell her this, she will automatically path to the nearest double bed and proceed to sleep. She will stay there until you sleep too. When you wake up, she'll give a pillow talk comment.

Friendship

When Serana first meets you, she'll initially be closed off and guarded. She won't be talking much. However, as you adventure more with her, complete more Dawnguard quests, or just talk to her a whole lot, she'll eventually start warming up to you and becoming more carefree and open.

Training

When you've become friends with Serana, she'll now be able to train you once a day in any of the following skills without any fees (Alchemy, Speech, Conjuration, Destruction, Light Armor).  She doesn't train you in anything else, as these are skills she's naturally proficient with.

Reciprocal Training: Elevate Serana's combat prowess by training her in specific skills—namely Block, Archery, Heavy Armor, Two-Handed, and Sneak—as long as you've mastered them (at least level 40). Remember, these are practical, NPC-applicable skills; so, no Blacksmithing! Wondering about Alchemy, Speech, Conjuration, Destruction, or Light Armor? Serana's got those covered; she's already a pro!

You can also train Serana in skills she's already knowledgeable in (like magecraft), considering your skills are a high enough level yourself (again, at least level 40)

Teleport 

After you have a small conversation with Serana, she'll give you a spell which will allow you to teleport her to you at any time. So if she ever gets lost or stuck, you can have her join you in a jiffy! (This spell is removed during specific quests, like the end of the Main Quest, since those quests were intended by the developers to be done without a follower).

Drinking Buddies

At any player home or inn, you can drink with Serana (both alcoholic and non-alcoholic drinks), and have casual and immersive talks over a multitude of topics. The player can have this both seated and standing (at their behest). The player also gets a bonus perk for completing these talks, which gives small buffs for 24 hours.

Gift 

A gift-giving feature, which allows the player to give Serana different types of gifts- any item basically. She will react positively to alcohol, flowers, and high value items- but negatively to the rest. Serana can give you gifts as well.

Blood Potions

Serana now drinks blood potions from her inventory every 24 hours or so, considering she's still a vampire. If the player is a vampire as well, they can ask Serana for Blood Potions. Her inventory will automatically be replenished.

Serana Hood Fix

You can ask Serana whether you want her to keep her hood on or not. You can tell Serana to never equip it at all, or only to equip it if it's daytime and she doesn't have any other headgear. 

Follow Distance Config

You can change how far or near you want Serana to travel along with you! Serana will also be able to travel beside you, should you ask her to do that. Additionally, for the close beside feature, you can ask Serana whether she'll do it only as you're adventuring, or all the time. 

(Follow beside based on code by Followers as Companions by Ishara Meradin)

Serana Outfit Feature

Serana can wear whatever you want her to wear! No need to use another outfit mod/follower framework feature, or fiddle with the lackluster vanilla system. You can set adventure, home, and city outfits, which she will automatically cycle between depending on the location she's in. 

Serana Backpack Feature

Serana can store items in a dedicated storage inventory without using or equipping them. Gone are the days of Serana using stuff you don't want her to use!

Custom Horse Support 

Serana now has her own custom horse, which you obtain through a short quest (which can be triggered as early as the Moth Priest hunt). You can also choose between two name options for it- "Phoenix" and "Nightshade" as decided from a Patreon poll. Whenever you mount your own horse, she will mount hers in turn. The horse will also follow/teleport to her when it has gotten too far, so no need to worry about horse catch-ups. After this update, SDA will now be incompatible with other mods that give Serana custom horses/custom horse support, like Convenient Horses (but a patch for that mod will be provided).

Home-Cooked Meals 

Serana can now cook home-cooked meals for you, similar to how vanilla spouses can. You do not need to romance Serana for this.

Spell-Teaching 

You can now teach her spells (from a select list of vanilla spells). Mod support from mods like Apocalypse is eventually planned, so stay tuned for that! Just speak to Serana (as long as you know the spell) and you can teach it to her right away. Giving her a spell book will not work. You can also enable or disable Serana using these spells at will.

In addition (after a short conversation with her about her spell-casting abilities) she will gain access to an expanded repertoire of new spells, like Healing, Oakflesh, and Flame Atronach. These spells are leveled, so as Serana levels up she will gain access to more powerful variants of these spells. I mean- it doesn't make sense for a vampire thousands of years old to only know a measly Vampire Drain and Raise Zombie, right?

Custom Names 

If the player is named a certain name that has been requested by Patrons, Serana will automatically recognize that (if on PC), or manually if on console. She will then call the player by their custom name! (See the article here for all the names)