Aside from both being fantasy/romance/mystery, both gave me similar vibes, but they do have some differences.

Similarities:
- Both are Fantasy/romance/mystery dramas, with more mystery in the beginning and more romance towards the end
- Both have creepy fantasy elements and involve heavy emotions/decisions which gives them a similar vibe at times
- Both involve a non-human character
- Both dramas involve a main character looking for their parents/parent
- Both involve exploration of afterlife, gods, and have similar depictions of the journey to death (on a boat in a river)
- Both dramas involve quite a bit of saving

Differences:
- While TOTNT has some historical backstory, it is set in modern time and Arang is set in Joseon time
- Arang involves more slow burn romance where TOTNT the main characters fall in love much more quickly
- While Arang also has fun side characters, it feels much more contained/focused on the main characters while TOTNT has more of an ensemble cast feel

I would recommend these dramas if you think the similarities are why you liked one or the other drama, but if the things that are different between the dramas made you like one or the other drama, I would be hesitant to recommend it.

While I was watching TOTNT, I was reminded of Goblin very strongly. They share very similar vibes.

- Both have similar themes of reincarnation, destiny, love, and impending death
- Both are fantasy/romance
- Both male leads are supernatural characters with god-like abilities and have been waiting for the female lead for hundreds of years
- Both have similar themes of love against destiny
- Both have great cinematography
- Both mix scenes that are meant to feel very epic/grand but also have comedic scenes
- Both have several interesting side characters
- Both female leads are doomed with death through similar systems, more so in Goblin
- Both main couples (imo) are underdeveloped and quickly fall in love, but that might be preferred for someone that dislikes slow burn romances

These may not appear to be similar, but I was reminded of LOTBS when watching Extraordinary You. LOTBS is more serious while Extraordinary You is fluffier, but both dramas have:
-funny/spunky female leads
-cute romance but with sad/emotional scenes sprinkled in
-parallel timelines (joseon/modern) in which ML and FL were in love. In both dramas the ML is aware of the parallel timeline and tries to change their destiny
-amnesia