Notes:
I can't even remember who was actually playing it apart from Olors as he was the DM for the sessions, which is why I haven't included anyone else apart from myself in this. This was back when I was very new to the site, so probably two years ago now, but in theory the thread should be in the Fun Archive somewhere if you want to go and hunt it down.
All I remember is that we had just gotten directions from Muffet after solving a lever puzzle and then we were suddenly in Apocalypse Now: The Anime.
The sources used are listed in order of appearance and aren't hyperlinked as I don't think the character limit if large enough for me to do so.
Hedgie: https://www.123rf.com/photo_98517847_little-cute-cartoon-hedgehog-with-an-umbrella.html
Snowdin before attack: https://www.deviantart.com/bakenius/art/Snowdin-Undertale-580219672
The Fire Nation Attacks: https://www.youtube.com/watch?v=JaeFrq7Lj2o
Signalis STAR: https://www.reddit.com/r/signalis/comments/10897vr/a_fanart_of_a_star_unit_i_commissioned_artist_is/
Door Gunner: https://danbooru.donmai.us/posts/1051992
Door Gunner Background: https://twitter.com/Natalie06788907/status/1242544617968537600
Flowey: https://aminoapps.com/c/undertale/page/blog/flowey-has-emotions/PRJi_mu71pMD5JmdJ3xVEEq8oMoPBm
AK47: https://www.freepik.com/premium-vector/black-white-illustration-ak-47-rifle_15982751.htm
Burning Town: https://undertale-chronicle.fandom.com/wiki/The_War_For_Humanity
Neco-Arc: https://www.youtube.com/watch?v=DRXFQxuhhyo
Dirk: https://www.pngegg.com/en/png-whhvh
Bullet Hole 1: https://www.hiclipart.com/free-transparent-background-png-clipart-zkbpi
Bullet Hole 2: https://www.clipartmax.com/middle/m2i8Z5N4i8K9H7i8_clipart-bullet-holes-png-download-bullet-hole-texture-unity/
Bullet Hole 3: https://imgbin.com/png/5urfhc26/bullet-holes-png
Sans: https://pixelartmaker.com/art/cb0012bf105ca16
Undyne: https://knowyourmeme.com/photos/1111762-undertale
Burning room made using DALL-E 2: https://labs.openai.com/e/UAwjNwdotr3hf5iJrQmtOqiS
Mettaton: https://www.pinterest.co.uk/pin/399976010635920816/
Bullet Holes: https://freepngimg.com/png/24904-gunshot-transparent
Wakizashi: https://www.deviantart.com/seventh-samurai/art/Katana-with-Wakizashi-2-25412450
Rubble pile made by using DALL-E 2: https://labs.openai.com/e/2RY1fNWWtRRJVxw2vAwYT0Kf/W7rn92r7HDoy9ijuqReziuyR
Frisk: https://www.pinterest.co.uk/pin/441634307204323374/