Fairly Simple Changes to the vanilla spells,perk,magic effect.
As you know ,the Invisibility abilities in vanilla game are too overpowered.With sneak or illusion skill high enough, you can just use the abilities to defeat any enemy without being attack or taking any damage. 

"Invisibility" ? The "Invincibility" might suits it well.


Detail:

1.Invisibility:(Expert Lv75 Illusion spell) 

Now when you cast the spell,a side effect will come along with the invisibility.You can't deal any melee damage using any weapon during the invisible effect.

(The goal is to prevent the build I call "Illusion Assassin" from abusing.
Since in the vanilla game you can hold the Invisibility spell in one hand while performing sneak attack with dagger in the other hand.And after the sneak attack,you loose your finger to cast the Invisbility.Then,the Invisbility become "Invincibility". )

2.Shadow Warrior perk:(Lv 100 Sneak tree's perk) 

Now the invisibility last 2 seconds and has 8 seconds cooldown time. 
(It means now you can't spam the "Crouch" button to be invisible and invincible like cheating, killing everyone in sight without any side effect.)

3.Nocturnal Cloaks:(The one from the Thieves Guild questline.) 

Now you can't use it in combat.But it's changed from power to lesser power for constant usage,requiring 50 magika to cast.
(It means you can now be invisble all day if you are a Nocturnal's shadow agent.But unable to use it in combat.)


4.Vampire Invisibility:  
 Now the vampires can only use the Invisbility during wee hours.(0AM-5AM)Unable to deal melee damage while invisible too.  Effects npcs and mods if they use the vanilla magic effect.
(That is to prevent you becoming "illusional assassin" too early.It wasn't need any skill grade to cast the powerful Invisibility if you are a vampire! You just need to don't feed for a few days! WTH)

5.New spell:Shadow Aggression:
(Lesser power,requires Master lv100 Illusion skill)

It's a invisbility spell as lesser power.It lasts 5 seconds and has 20 seconds cooldown time. You can use it to perform sneak attacks.Can be purchased from Drevis Neloren in Winterhold after you finish the Illusion Ritual Spell quest.
(Usage: Cast the original Invisibility and sneak through the way. When you are ready to deal with enemy, draw your dagger and cast Shadow Aggression ,perform attack , cast Invisibility spell, wait for the cooldown on you way.)


6.Now they are balanced !

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Compatiblity: Anything edits or overwrites the spells and magic effect will conflict with it. And if anything overwrite the illusion ritual spell levellist,the new spell book will not appear in game (just use console or tesvedit).

Installation:
Unzip the files and put them into your Skyrim/Data folder.

To Uninstall:
Simply remove the files,only 2 simple scripts and 1 esp.




Credit:

Withe01 for the invisible cooldown script:
https://www.nexusmods.com/skyrim/mods/54397


Recommand Mods : (For balanced vanilla style gameplay)

Invisibility and Eyes Mesh Fix :
https://www.nexusmods.com/skyrim/mods/43055

Balanced Magic:
https://www.nexusmods.com/skyrim/mods/2275

Stealth Skills Rebalanced - Sneak - Lockpicking - Pickpocket:
https://www.nexusmods.com/skyrim/mods/28418