Spoiler warning: Spoilers for Season 1 only. Later-season identities and developments are not revealed.
Tyler is the Hyde, and Marilyn Thornhill is Laurel Gates, the woman directing his attacks. Wednesday Season 1 resolves the murders through that partnership, then uses Wednesday’s new phone to show that solving one case has not ended her exposure to danger.
What is Laurel trying to achieve?
She continues her family’s campaign against outcasts and gathers what she needs to resurrect Joseph Crackstone. Wednesday’s blood is the final requirement because of her connection to Goody Addams, who sealed him away.
Laurel’s apparently harmless place inside Nevermore gives the plan access to the people it targets. The reveal makes belonging to the institution a useful disguise rather than evidence of loyalty to its students.
Tyler is not simply an unrelated monster who happens to be nearby. Laurel exploits his hidden heritage and his need for answers about his mother, then gains a willing participant in her plan.
How does Wednesday survive the finale?
Goody passes through her to heal the wound Laurel inflicts, at the cost of Wednesday losing that connection to her ancestor. The students then defeat Crackstone’s attack on Nevermore.
Principal Weems is killed after using her shape-shifting ability to help expose Laurel. Her death is a real loss within the first season’s conclusion, not a trick that can be dismissed because disguise is part of the episode.
Wednesday’s survival also depends on relationships she has repeatedly resisted. Her unusual independence does not provide every skill or every piece of information required to stop the plan.
Who sends the last messages?
Season 1 does not identify the stalker. The photos and threat establish that someone is watching Wednesday; they do not provide enough evidence within this season to name the sender.
Later-season answers belong to a different spoiler scope. They should not be inserted into an explanation that promises only the first season’s evidence.
The change of device is a precise final joke with consequences. Wednesday receives a means of connection she has largely avoided, and it immediately becomes a route through which another person can reach her.
Crackstone’s resurrection plot has ended. The phone introduces a new problem instead of proving that the earlier solution was false. The case is closed; the attention Wednesday attracts is not.
Sources: official ending breakdown; official interview or additional context.