One of the oldest spells, created long before The Borders were set. Now, after world noticed real consequences of it, it has been forbidden and using it is punishable by torture and death.

Forbidden

Two creatures are merged into one being, saving them from ultimate death, often 'curing' them from different diseases and, can give them additional abilities that one of merged creatures had but other had not.

During merging a new body and soul is formed- from most dominant characteristics that belonged to merged creatures. What it's going to be and how it's going to manifest/look like can't be determined until merging is finished.

Merged/created might become more resistant and hard to wound/kill- this can be a positive or negative, depending on the individual and what they have become.

Takes great physical and mental toll on the merged/created creature. Their appearance is nothing like it used to be, which can make them not accepted in society. Their character is also different to what it was, thoughts and voices inside their head can be conflicted, turning them insane.

Both of participants need to be inteligent creatures, that are able to communicate with other races (humans, Syrinx, Dragons, etc.)
Both of the participants need to be consenting to be merged.
Both of the participants must be very ill, wounded, or in other ways close to death - so that it is known that they wouldn't survive long without Life-Merging.

Morality of this Spell has been discussed since first time it was used. It's true that it gives dying beings a new chance to live, but they are nothing like they used to be before. Some people used to think that it's better to die then to be turned into a monster- others thought that not only it can save someone, it can also give them new abilities, if Merging worked in their favor.

At the moment Life-Merging is considered to be unethical and has been strictly forbidden not only on main continent, but also in every other part of the Ziophiphere Realm.

Back in the Day people who could succesfully use this Spell were considered to be the biggest and wisest wizards and Scholars in the whole World.
Today, as the spell is forbidden, users of it are considered to be cruel, crazy, or lying.

It needs three participants- someone who is going to use/cast the spell, and two consenting bodies, creatures, that are close to dying and would not survive without being merged.

This Spell isn't healing spell. It cannot cure wounds. It simply merges one creature with another, creating a new body and soul out of more dominant characteristics of each one of them. Sometimes it means that wounds dissapear, sometimes it makes them heal, sometimes it doesn't help at all.

This Spell does not bring dead to life.

This Spell cannot be undone.

One of the many reasons this spell was finally forbidden was Pandragon himself. Since he was the son of King and Queen, his first years of struggle in new body was observed by the public. Later, when he ran away and later reappeared to claim the throne, he seemed to be nothing like he used to be. Everyone thought that he had gone insane- but it was quickly discovered, that it is impossible to take away his crown and power, and due to long lifespan (he got from being merged with desert dragon) waiting for his death became pointless.
Graenne finally accepted their faith and new king, but Scholars and Wizards from around the World, who wanted to make sure similar situation is not going to happen again, have decided to forbid the spell and burn all the books that had it mentioned.
If there's still someone who remembers how to Life-Merge, and will use it, they will be punished by torture and death.