Alright then, let's jump right into it. The dark brotherhood needed a bit of sprucing up so i hope i did right by them.

Here goes:

First of all, let's start of with their leader, Astrid.
Normally she levels with you quite high (infinitely i believe) and she starts at level 10. (which is to my opinion to low.)
Changes:
1) She starts at level 25.
2) She levels with you to level 90. At a rate of 1.2 to your 1.
3) She has the following perks. (armsman60, agiledefender40, stealth40, assassinsblade and illusionexpert)
4) Added the spell invisibility.
5) Added an ebony dagger to her inventory. (And yes, she dual wields)

Next we have Arnbjorn, and yes he needed it.
Changes:
1) Changed his combat class from assassin to barbarian.
2) Now levels with you from 15 to 75.
3) Changed his main weapon to an ebony battleaxe, and added an ebony dagger and skyforge steel battleaxe to his inventory. (he was a part of the circle)
4) Gave him the perks. (barbarian40, agiledefender40, armsman20, muffledmovement and silence.)

Next we have Festus. He originally leveled with the player to level 50.
Changes:
1) Changed his combat class from assassin to combatmagedestruction.
2) Now levels with player from 15 to 75.
3) Added 600 to his magicka offset.
4) Added perks. (Elemental potency, recovery50, regeneration, magicresistance70, augmentedflames60 and stealth40.
5) Added spells. (conjure flameatronach, conjure dremora lord, invisibility)
6) Changed his dagger to an ebony dagger.

Next we have Gabriella.
Changes:
1) She levels with the player from 15 to 75.
2) Added 2 ebony daggers to her inventory.
3) Added firiniel's end to her inventory. (Only to her inventory when she is alive. The dead one after the sanctuary attack should not have one.) Reason for that is because you already should get it during the questline. So if you chose to kill them instead you should still get it.
4) Added the perks. (Overdraw60, armsman40, stealth40, muffled movement, backstab and illusion expert.
5) Added the spells. (fast healing and invisibility)

Next person is Nazir. From what i know he leveled with the player to lv 50.
Changes:
1) Now levels with you from 20 to 80. At a rate of 1.1 to your 1.
2) Added an ebony dagger to his inventory.
3) Gave him the perks. ( agile defender60, armsman40, muffledmovement, dualflurry and illusionexpert.)
4) Added the spell invisibility.

Next person is Veezara. He normally levels with you to level 50.
Changes:
1) Levels with you from 15 to 75. At a rate of 1.1 to your 1.
2) Changed default equipment to elven sword and ebony dagger.
3) Gave him the perks: (armsman40, agiledefender40, dualflurry, dualsavagery, savagestrike and muffledmovement.)
4) Also gave him the spell invisibility.

Liz the spider. What can i say, she is a spider.
Changes:
1) To make her a bit more threatening i upped her level cap to 35.

Next person is Cicero.
Changes:
1) He will now level with you from level 20 to 90. (Why so high? That is because he is efficiently Astrid's counterpart in the brotherhoods politics.)
2) All versions of him should now have 2 ebony daggers.
3) Has the perks. (armsman40, stealth40, overdraw20, muffledmovement, lightfoot and illusionexpert.)
4) Added the spell invisibility.

Next are the dark brotherhood initiates.

The male one is now called Kain.
1) Levels with you from 15 to 75.
2) Changed to combatmagedestruction.
3) Changed outfit to dark brotherhood robes.
4) Gave him the perks. (armsman40, muffledmovement, lightfoot, illusionexpert, augmentedshock60, quietcasting and recovery50.)
5) Gave him the spells. (invisibility, lightningbolt, chainlightning and fasthealing.)

The female one is now called Luna.
1) Levels with you from 15 to 75.
2) Added an elven bow, elven sword and 35 elven arrows to her inventory.
3) Gave her the perks. (armsman40, agiledefender40, overdraw20, muffledmovement, lightfoot, illusionexpert and stealth40.)

A few changes have been made to some combatclasses, namely the combatassassin and the lightarmormastertrainer.
Changes:
1) This goes for both of them and is actually the only change made, i switched the leveling in the alteration skill to leveling in the illusion skill instead.

I guess that was it.
As for the requirements.
They are:
Skyrim
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