[WARNING: there will be captcha related to the codes shown here. If you feel strongly against about it, I suggest you take it up elsewhere...]

That said, we've had 2 subscriber's e-mail in this present promotion (halloween 2019), which I'm gonna list below. The discounts are a bit better than what you get on the regular sale.

1) Image with hidden codes:
(there be spoilers if you wanna find them by yourself)

- top right corner: Grim Dawn (75% OFF)
- middle: Diablo + Hellfire (20% OFF)
- lower left corner: Hollow Knight (-55% OFF)
- top right corner: Bloodstained: Ritual of the Night (15% OFF)
- lower left (around yellow, green, purple stuff): Blasphemous (20% OFF)

If people wanna post their codes directly here in this thread, feel free to! (mine were taken, I think).
Also, check this thread, there there may be more codes untaken there:

https://www.gog.com/forum/general/halloween_sale_blair_witch_layers_of_fear_2_call_of_cthulhu_and_300_deals_up_to_90_41594/post96

2) Just "now", we've had a "exclusive" Frostpunk discount - the highest discount have ever had (60 % OFF), time-limited to 40 hours from now.

Again, feel free to post your codes codes directly in this thread, if they aren't being used!