I succeeded in finding all 7 people who were in the entrance hall afterwards, although this game can be completed without discovering all of them.
0:00 Opening
1:54 Seven people
3:36 Sam is dead
4:10 Joe in cemetary
9:57 Sally is dead
11:20 used text mode
12:51 Green is dead
13:52 Bill is dead
16:03 Tom is dead (used text mode)
20:06 find the murderer (used text mode)
23:14 get jewels
It is a historical piece. It was played in a rush. There are seven people in the mansion at first. They are being killed for a treasure hidden somewhere in the mansion. Who is the murderer and where is he? Dying messages suggest the murderer.
くしかつ Kushikatsu currently has 694 views spread across 3 videos for Mystery House. There's close to an hours worth of content for Mystery House published on his channel, less than 0.98% of the total video content that くしかつ Kushikatsu has uploaded to YouTube.