I played D2 regularly all through my teenage years. I think it might be one of the most exploited games ever which was half of what made it fun:
* There were a variety of ways to duplicate items online. One really popular and well known one involved spamming bone wall on a necromancer + meteor on a sorceress which would cause the server to lag to the point that your ping would exceed 1000. At that point, you could join a game with the same character, stop spamming the skill so your original character didn’t lag out, thus creating two ephemeral copies of your items. This eventually got patched
* One commonly duplicated item was called a stone ring of Jordan (SOJ). They were so commonly duplicated that blizzard added an event that if you sold ~100 to an in game merchant, everyone connected to a given server would spawn an Uber version of Diablo that dropped a unique small charm.
* Another way blizzard got rid of duplicated items was something called “rust storm” where they’d take the servers offline and go through every item in existence, deleting duplicates.
* Botting was extremely common. There are a bunch of weird quirks added to the game to try to prevent botting, though none of them worked. For example, if you spin the mouse wheel while hovering over a skill, it’ll cycle through your skills. That would immediately get you kicked from the game because the person who programmed the server thought only bots could switch skills that quickly.
* There was a feature in the game that if one person in your party got a quest, the whole party got the quest. Players regularly abuse this to “rush” level 1 characters into act 5 in the hardest difficulty so that they can expedite leveling up.
* There are ethereal items that get a 50% bonus to their core attribute (eg. Armor). If you used the cube recipe to socket the item, that 50% bonus would then get applied again. There were an entire class of items called “ebugged” that were overpowered.
* There was an event added much later for a unique large charm. Someone figured out that you could trap Mephisto in a building such that he would never path out of it, continuously trigger him to summon minions, and kill those minions to grant you massive experience with low risk of death. Thus uber leveling was born. You’d do this in a party with a fully equipped character handling the minions and could go 1-80 in like 5 minutes. This later got patched.
* There are still a small group of people who maintain items from previous patches that no longer spawn. A good google search term for this if you wanted to go down a rabbit hole is “1.08 valkyrie wing”. These are commonly duplicated and at risk of disappearing in a rust storm, so these players maintain a genealogy on forums of their items to prove they’re “legit” and not going to poof on you.
* Servers would drop you after like 30 minutes of inactivity. However, there were pathing bugs that could be exploited to make your character bounce back and forth between squares on the grid effectively preventing you from disconnecting. No mouse clicking scripts needed.
There’s probably more but this is getting long