Both are psychological & creepy but pigpen is more dark. The beginning of it will give kinda strangers from hell vibes somewhere. You'll feel those ominous & spooky vibes as you have felt in strangers from hell. & yeah gaslighting stuffs is here too with a bunch of creepy & strange people.

Plot is very similar to ATCY.
-FL is depressed & regrets for not able to save ML.
-FL sends letters to her past self (high schooler) so that past will change & ML will be saved.
-ML & FL met during their high school times & eventually liked each other tho there are many problems were going on.
-There are also sweet friendship moments.
-This is not exactly mystery or thriller, rather I would say it showed more of a psychological aspect of the story.
- If you are sensitive, prepare tissues cause this is really emotional.
If you liked ATCY, must check this out!

Tho it has similar theme such as time loop/time travelling, plot is different.
-Both ML & FL time travel to past in order to change their past
-FL prevents death of ML by time travelling to past
Similar theme is used but plot is bit unique, we have seen a lot of high school time travelling drama but this is different. If you like time travelling drama such as ATCY, SOOD... You should try this!

If you want to watch something similar to ATCY, this movie has also similar story
-Similar theme
-Time travelling
- Story is about high school love story
-Both ML & FL time travelled (both past & future) through music (playing piano)
- time travelling to 90s