The most common lament on forums like Reddit’s r/diablo2 is: "I have my discs, but I lost the CD key 15 years ago." If you are in this boat, here is your strategy guide.
For a (like PlugY or PD2), the feature could be: diablo 2 original cd key
You use that key for anything that pings Blizzard's modern authentication servers. The most common lament on forums like Reddit’s
Check the back of the "jewel case" or the inside flap of the box. The Manual: diablo 2 original cd key