New difficulty mod in Stardew Valley will purge your saves if you use a guide
On what date was the high difficulty mod created?

The high difficulty mod for Stardew Valley was created on June 21 by software engineer Sylvie Nightshade1. This "hardcore" mode deletes players' save files if they use a guide while playing the game on PC.
What additional feature did Nightshade add to the mod?

Nightshade added a feature to the mod that scans the title of every window or tab open while Stardew Valley is running. If any window title includes "Stardew Valley Wiki" in the title, it erases the player's save file and closes the browser window the wiki was found in.
What is the consequence of having a window titled "Stardew Valley Wiki" open?

The consequence of having a window titled "Stardew Valley Wiki" open while playing the game with the high difficulty mod created by software engineer Sylvie Nightshade is the deletion of the player's save file1. This mod, considered a "hardcore mode," was designed to scan all open window titles and if it finds "Stardew Valley Wiki" in any title, it erases the player's progress, forcing them to start over without the use of a guide1.