Necromage is a Restoration perk that makes all spells more effective against undead. Specifically, it increases the magnitude by 25% and the duration (if applicable) by 50%. Since vampirism makes the player undead, this means that any spells and other effects that you use on yourself are also augmented by Necromage. For example, healing spells are 25% stronger and flesh spells are both 25% stronger and last 50% longer. However, Necromage Vampirism also makes negative effects on you 25% stronger, such as the stat reduction from your weakness to sunlight as a vampire.
Note: From this point forward, I will refer to Necromage Vampirism/Vampire as simply NV. Furthermore, also note that in order to receive the effects that being an NV has on something, be it a perk, standing stone, or anything else that NV affects, you must be an NV before receiving that effect. For example, in order to receive the effects that NV has on the Atronach perk, you must be an NV before selecting it.
– Atronach is increased from 30% to 37.5% Spell Absorption.
– Avoid Death is increased from 250 to 312.5 health restored.
– Dual Flurry is increased from 120/135% (in other words, 20/35% faster) to 150/168.75% (in other words, 50% to 68.75% faster).
– Extra Pockets is increased from 100 to 125 extra carry weight.
– Fists of Steel is 25% more effective, with the specific damage increased depending on what gauntlets you’re wearing.
– Magic Resistance is increased from 10/20/30% to 12.5/25/37.5% Magic Resistance.
– Power of the Grave is increased (Vampire Lord perk) from boosting health/magicka/stamina 50 points to 62.5 points.
– Power Shot is affected, but I've heard conflicting reports as to whether it affects stagger chance or stagger duration.
– Quick Reflexes slows time down more.
– Quick Shot is increased from 130% (in other words, 30% faster) to 162.5% (in other words, 62.5% faster).
– Recovery is increased from 25/50% to 31.25/62.5% more magicka regeneration.
– Shadow Warrior lasts 50% longer (about an extra second).
– Steady Hand is affected by NV, but in this case it’s a bad thing since it keeps you from shooting arrows effectively while zoomed in, so either perk Steady Hand when you’re not an NV or don’t perk it at all.
– Wind Walker is increased from 50% to 62.5% stamina regeneration.
Important to note is that while NV does not affect Mage Armor directly, the AR boost that NV gives to flesh spells is multiplied by Mage Armor. For example, NV gives you an additional 25 AR on top of the usual 100 AR from casting Ebonyflesh but if you cast it all three ranks of Mage Armor it gives you an additional 75 AR on top of the usual 300.
– The Atronach is increased from 50% Spell Absorption, 50 Magicka, and -50% Magicka Regeneration to 62.5% Spell Absorption, 62.5 Magicka, and -62.5% Magicka Regeneration.
– The Apprentice is increased from 100% Magicka Regeneration / Weakness to Magic to 125% Magicka Regneration / Weakness to Magic.
– The Lady is increased from 25% Health/Stamina Regeneration to 31.25% Health/Stamina Regeneration.
– The Lord is increased from 50 AR and 25% Magic Resistance to 62.5 AR and 31.25% Magic Resistance.
– The Shadow is increased from 60 seconds to 90 seconds in duration.
– The Steed is increased from 100 Carrying Capacity to 125 Carrying Capacity.
– Become Ethereal is increased from 8/13/18 seconds to 12/19.5/27 seconds in duration.
– Call of Valor is increased from 60 seconds to 90 seconds in duration.
– Elemental Fury is increased from 130/150/170% weapon speed (in other words, 30/50/70% faster) to 162.5/187.5/212.5% weapon speed (in other words, 62.5/87.5/112.5% faster). The duration is also increased from 15 seconds to 22.5 seconds.
– Slow Time is increased from slowing time down to 30/20/10% of its normal speed to 22.5/15/7.5% of its normal speed. Also, the duration is increased from 8/12/16 seconds to 12/18/24 seconds
– Dragon Aspect is increased from 5 minutes to 7.5 minutes in duration, shout cooldown reduction from 20% to 25%, and AR from 100 to 125. More parts of it may be affected, though I can’t really say for sure with console testing.
– Candlelight is increased from 60 seconds to 90 seconds in duration.
– Waterbreathing is increased from 60 seconds to 90 seconds in duration.
– Flesh spells are increased from 60 seconds to 90 seconds in duration. Furthermore, all flesh spells give 25% more armor rating.
– Dragonhide is increased from 30 seconds to 45 seconds in duration.
– Bound Weapon spells are increased from 2 minutes to 3 minutes in duration.
– Summon spells (Flame Atronach, Mistman, Dremora Lord, etc.) are increased from 60 seconds to 90 seconds in duration.
– Cloak spells are increased from 60 seconds to 90 seconds in duration. Magnitude might also be increased by 25%, but again, being on console limits my ability to test it.
– Muffle is increased from 3 minutes to 4.5 minutes in duration.
– Invisibility is increased from 30 seconds to 45 seconds in duration.
– Healing spells heal for 25% more health.
– Ward spells are 25% more effective.
Note that the NV bonus applies regardless of whether the spell was cast normally or through a scroll/staff.
– Armor enchantments are 25% stronger.
– Potions and Foods are 25% stronger and last 50% longer.
– Temporary blessings are 25% stronger and last 50% longer.
– Greater and Lesser Powers are 25% stronger and last 50% longer.
– All passive bonuses or penalties from active effects (such as Agent of Mara, Seeker of Sorcery, or Weakness to Sunlight) are boosted by 25%. In order to receive the NV boost to racial passives (such as a Khajiit’s Claws), once you become an NV, transform into a Vampire Lord and change back. Once you do, the boost from NV should be applied.
– Your Vampire Lord AR is boosted by 25%, as is the inherent health/magicka/stamina boost that the Vampire Lord gives.
For those of you who play on PC with the Unofficial Skyrim Patch, the NV glitch is fixed, meaning that Necromage won't make your perks, enchantments, and the like stronger when you're a vampire, but there's a mod that "unfixes" it, enabling you to take advantage of it again.
Disclaimer: Most of this guide has been the product of research on the internet; I wrote it back before I had Skyrim on PC which limited my ability to test a lot of things. I can't guarantee that everything here is completely accurate.
Finally, I’d like to note that this guide is not necessarily 100% exhaustive. If there’s something affected by NV that I missed, then let me know in the comments below.