Nicky's Rio son too.

I feel there were so many lines that imply this and the finale is starting to make more sense - especially because the dandelion in the trial!

Jen explains that Green Craft™ is about the cycle of all living things - growth and decay in constant flow. So it's not just about dying but being born too.

So it would track that Rio's love for Agatha was so strong that it actually created life - Nicky. However, there would be consequences to this because proper balance had to be maintained somehow. Rio probably even warned Agatha about it, but Agatha always believes she is above the rules so in her head she probably thought she had every right to Nicky (maybe even her "prize" that she alludes to in their final confrontation). This would really add to Rio's hurt - Nicky was her son too. She thought she was giving Agatha a gift of life, but instead Agatha sees her as this cruel "evil" that "gave her nothing". To her Rio is the one who just "took."

It feels like it is also implied by Rio at the start of the episode when she says "This walk with another woman's son on a road that doesn't...". She could be referring to Nicky being her son.

But I think Agatha finally accepts her truth during the final trial when she sees the dandelion seed in her cameo. She even says "Out of Death - life" as she grows it because she finally understands the literal implications of that phrase.

That Dandelion is representation of Nicky. And sure enough, as soon as the flower grows and blossoms, it quickly enters the final stage - when it turns into the seeds that can be scattered by the wind again and continue the cycle of life. Because guess what, "dandelions produce seeds asexually by apomixis, where the seeds are produced without pollination, resulting in offspring that are genetically identical to the parent plant".

When Nicky is born, we could probably assume it was indeed asexual reproduction - Agatha says she didn't use a spell or incantation, but instead he was made from scratch (obviously a clever nod to his name). On one hand it could be read like Agatha is astonished how something this magical could happen without actually using any witchcraft. However, this also feels like a suggestion that maybe she is just amazed at how he could possibly exist. Kathryn Hahn in her recent interview alluded to how the witches didn't need men, babies were just born. So it was Rio's "dandelion seed" that made it happen.

It is the second characteristic of dandelion species is what seals the deal for me - "the offspring being genetically identical to the parent plant". Nicky as the offspring of Death needs bodies to survive in this realm. During his birth Rio says she can offer only time, because she can maintain the balance, as long as Nicky gets his bodies.

That's why she hates Rio and calls her evil - not because of Rio herself, but because of what her "genetics" did to Nicky. Agatha would rather have people believe that she is this evil witch killer that traded her child for the Darkhold, than anyone to know the awful truth that it was Nicky who was the cause of the killings.

In the flashbacks, there are those remarks about how they haven't "eaten for days" and that whenever Nicky was poorly he said he was hungry. Agatha said she couldn't create the food for him (and protect him from what's coming). She could've cooked that goat they had with them if they were really that hungry (btw, I still believe that goat is Senor Scratchy), but that wasn't the "food" that Nicky meant.

And just like Billy, Rio couldn't just take Nicky. He had to "turn himself in". It was his choice not to kill any more witches. On the day Nicky dies, he says "My mother needs me home". I think he is talking about Rio here, since he usually calls Agatha "Mama". This is the moment the decides for himself and goes home to Death.

I feel like this opens the possibility that we will indeed see Nicholas Scratch in the future (and have a role similar to the one in the comics). That maybe even he might not have "died" because he is an offspring of death, so he just exists in some Underworld realm, where he no longer needs bodies to survive. Maybe Agatha might have hoped that by killing more and more witches, she will bring Nicky back to life/this realm?

And the Ballad really was a protection spell she made for him too?

This would also be a more plausible explanation why Agatha went to kiss Rio when Billy asked "Is this how Nicky died?". I feel this was more of an apology to Rio for hating her for Nicky's treatment, because she finally understood why she had to do it?