RoM - Black Magic  

This mod requires the XML INJECTOR, THE SPELLBOOK INJECTOR 

This mod will allow you to get magical power by selling the soul of another character to the Old Gods. There will also be 3 new spells and various gifts that you will receive from the Old Gods, but if you anger them, you will become a vampire.

There is a small requirement before you can get into worshipping the Old Gods... a new book will be on sale when you install the mod:

Buy it, and read it, to unlock the option to purchase another book, a Weird Tome:

Buy and read the Weird Tome to unlock the option to sell a Sim's soul from a tombstone or urn:

Offering your first Soul to the Old Gods will make you a Worshipper.

As you keep going worshipping the Old Gods, things will happen... if you please them, they will give you new spells. Every soul you offer them will please them and give the spellcaster XP.

Get the happy enough, and they will unlock the first spell:

CONJURING (Jungle Adventure)

Conjuring allows you to Summon a Skeleton Servant by clicking on a tombstone/urn... 

The skeleton will stick around way longer than the JA adventure one.

Skeleton Butler can be summoned, too

And will behave exactly like a regular butler. The service is free (as long as a Witch or a Vampire are in the household) it costs just 1 otherwise (making it free causes LEs)

Perform it on self to become the vessel of the Old Gods... and collect souls:

Every soul you collect will give XP and please the Old Gods. You can also Drain Life, adding some days to your Sim's life while filling the other Sim's age progression (and more to come, I just need to figure things out). Possessed Sims are war machines without feelings, they can only kill and will not get sad or react to death.

Go too far in worshipping the Old Gods, and your Spellcaster will be corrupted by Evil Magic:

A corrupted Spellcaster gains XP a lot faster, has less feelings, they will also get red eyes and change a trait, it will be replaced by an evil one.

As they please the Gods, they will stop aging and become immortal.

LOSING THE OLD GODS FAVOURS:

If you stay too long without offering souls, you will lose the connection with the Old Gods... in the first phase, nothing will happen until you try to make an offering again... then something will happen... I'll write it in the comments to avoid spoilers. In the Corruption phase, losing the connection with the Old Gods will be much worse. You only get one chance with the Old Gods.

NON WITCHES

Regular Sims can read the books and unlock the ability to ask the Old Gods for Magical Power and become Wild Witches, they will also be worshippers straight away and have a bonus in the XP gain. From this point on, all works the same.

This is actually a Level 5 Practical Spell witches can unlock by Meditating on Magic on a stool. They will have to go in levitation to unlock it. This spell contrast the corruption, it will remove the corruption but also the magic, without the side effect of losing the Old Gods though. It also removes curses from self and from a target.

Notice: Vampires and Mermaids have no souls.

KNOWN ISSUE: sometimes, the urn doesn't have the option to offer the soul, this is because the stored sim is not instanced by the game. Calling forth the ghost fixes this problem.