Here is the full list of all 20 Saturnalia achievements.
Collect 3 tips from the Mouth of Truth
Complete Sergio's Mission
Complete Tecla's Act
Turn on all the lights inside the Mines
Complete Anita's Mission
Use a phone 5 times to gather your companions
Rescue a captured character 6 times
Use 100 matches
Complete Paul's Mission
Replenish your stamina 3 times while the Creature is chasing you
Light up all the bonfires in Gravoi
Read at least 90 clues
Run out of stamina 5 times
Find all the tools and consumables
Light all the votive candles in the church
Complete Claudia's Mission
Distract the Creature 5 times using the firecrackers
Flash the Creature 5 times
Team up with another character 3 times to reach a destination
Get captured while using a phone