casual filter

A part or stage in a game that escalates in difficulty in a very short period of time, separating the casuals from the actual gamers.

Not to be confused with a steep/vertical learning curve, as these mean that the game is hard to learn and master from the beginning.

Games with a casual filter will give you a false feeling of confidence as the filter comes after you have learned the basics and started progressing, just to catch you off guard and make your run end, usually having to start from zero again.

Some examples of casual filters in games include the winter in Project Zomboid and your first goblin raid in Dwarf Fortress