A chaotic co-op game where patients break out of a madhouse

S.E.M.I. (Side Effects May Include) Co-Op Available on Steam

October 18, 2025 Marc Szymanski

S.E.M.I. – Side Effects May Include… is a co-op game developed and published by Two Horn Unicorn. It is currently featured in the Steam Next Fest, where more than 35,000 players have tried the demo and over 22,000 have added it to their wishlists. As a result, the growing success has been entirely community-driven, achieved without publisher support. The demo is available now on PC through Steam, making it easy for anyone to jump in and join the fun.

In S.E.M.I., the team’s main resource is shared madness. During each match, anything can happen. A player might suddenly turn into a giant and wreck half the room, or go flying across it like a cannonball. Meanwhile, the game’s “pill” mechanic adds even more chaos by granting random powers with unpredictable side effects. For example, one player might shrink down and move quickly, another might grow massive and sluggish, while someone else might struggle to aim as their hands shake uncontrollably. In addition, the shared madness system can strike at any time, turning anyone into an agent of chaos.

Finally, each attempt ends with a personalized “medical report” that humorously diagnoses your playstyle and performance. With no keys or setup required, players can simply download the free Steam demo and dive straight into the mayhem.

What We Can Expect

Co-op gameplay focused on shared madness and unpredictable transformations
A “pill” mechanic that grants random powers with comedic side effects
Personalized “medical reports” for each player after every attempt
A community-fueled hit growing rapidly through word of mouth

My Thoughts

S.E.M.I. looks like the kind of game a group of friends could play for hours and have an absolute blast. The chaos and unpredictability are enough to keep the laughter going and make players eager for just one more round to see what new powers or side effects they might unleash. Since the demo is available now, grab a few friends, download it, and dive into the madness together. And before you do, check out the trailer!