You read that title right. Yes, you can actually finish the whole game, including the Lord of Destruction expansion, without attacking — known as a pacifist run. As it sounds, it is indeed quite difficult and only those who really know the game can do this. It is counterintuitive to what the game was designed for, but the fact that it can be done is in itself a testament to how good the game has been for all this time.
Players being able to do things like this is indeed a good thing for the game as it adds a new dimension to its gameplay that the designers most likely didn't even think about. It shows a degree of creativity and a lot of perseverance to pull off something like this. In this case, someone going by the name of DrCliche, a Diablo 2 speedrunner, did this impressive pacifist speedrun in 7 hours and 41 minutes. What makes it a pacifist run is the primary rule of never proactively attacking enemies at all.
What's allowed is passively damaging enemies with something like thorns or cast on hit Diablo 2 items. The first challenge comes from getting those items in the first place. A good character class to choose for this would be the Paladin due to the Thorns aura, which is the best way to damage enemies early on in a pacifist run. Other than that, the player would just be running past enemies to reach the next destination.
Things get tough once you get to the bosses since there's no other way to deal with them other than killing them. Since hitting them is not allowed in a pacifist run, you'll have to rely on them being hurt when they hit you, which is a tall order. You will also be doing a good amount of running away to heal up, which the Paladin can do with an aura.
The Necromancer may seem to be a good choice as well, but DrCliche's pacifist rules include not allowing summons or mercenaries to do the fighting for you. What DrCliche used was a Sorceress, which seems like an odd choice. But he was able to finish the pacifist speedrun in record time with that character class, and it was mostly about methodology rather than relying on the character's abilities.
The first thing you must do is find a Blood Moor spawn with the house with a chest that's close to the Rogue Encampment. It should also have a nearby shrine. That's quite specific, but that allows you to farm for 2 chipped skulls and chipped rubies, as well as amulets, rings, and a charm of strength. You can also farm for anything expensive so you can sell them for gold. The nearby shrine is for being able to get a gem shrine to upgrade the skull.
Upon getting a good bit of gold, you can go to Charsi and shop for a sash, quilted armor, and a Buckler of Thorns, as well as leather gloves and an equippable one-handed weapon of Strength. You can also get a Sash of Strength if there's nothing else. Everything else is a 2-socket small shield, 3-socket short bow for an Edge rune word, 2-socket caps for your chipped rubies, and a 2-socket Quilted Armor or Leather Armor for the Stealth rune word.
Those D2 items are for sneaking past enemies, damaging enemies passively, and so on. As you can see, this is fairly meticulous, and it goes to show that even after 17 years of existence, there are still some inventive things that can be done with Diablo 2.