Disclamer

First of all, bugged items are not actually bugged, they are just called that way in the community. These items are totally legitimised by Valve. So they are safe to buy and they are not going to get “fixed”.

History

Before Dota Reborn update in 2015 you could make rare sockets in some items and insert ethereal gems, but they almost gave no effect. After Reborn update, making such sockets became impossible, and since game engine was updated, effects started working.

Why are they so expensive?

They give special effects, for example ethereal gem “trail of burning doom” gives effect of burning hero (you can check how it looks like if you click on the item in bugged section). And also they are very rare. The most common bugged item has only 300 copies in the game.

Can I change effects?

Yes, but you will have to buy a different ethereal gem and insert it. When you do that, previous gem would be destroyed and you will receive new effect with new gem. Most popular gems with very visible effects are “trail of burning doom” and “ionic vapor”.

Why some of them cost 400$ and some 10 000$?

Mostly because of rarity, for example, bugged hand slot on morphling is very rare, about 20 copies in the game. And its also a great immortal slot. Some bugged items have bad slots, common or rare items which dont look good. When you have immortal bugged item, its the best. You can get effect also maintaining great set.

Are they worth it?

From my experience playing with them - yes.

Probably the biggest flex in the lobby. Streamers and pro players popularized them, so you would receive messages like

“wow are you rich?” or “why is your hero burning?” basically every game.