Update: To dispel all doubts, Bungie's Community Manager dmg04 has confirmed that what Witherhoard is doing now is definitely unexpected and will not be done forever. Sorry, folks.

Original story

Destiny 2: Season of Arrivals launched yesterday with new dungeons, activities, gear, and a new exotic grenade launcher called the Witherhoard. Available immediately to Season Pass holders, it packs quite a punch. In fact, it packs more punch than Bungie intended. Eager players who got their hands on it and actually used it found that it not only beat up raid bosses, but absolutely deleted them.

It is unclear exactly what is causing this glitch, but as streamer Fallout Plays noted on Twitter, it is not a "normal DPS type" effect. other streamers, including Sweatcicle and Cup, have been using their own raid bosses' insta-kills they have shared. You can see more in the video below: after taking a few shots in the jaw, Emperor Kallus suddenly goes down hard.

Grenade launchers fire Taken Blight. This effect does not stack when applied to most enemies in the game, probably to prevent teams from doing exactly this sort of thing. In other words, the damage stacks when applied to bosses, and in conjunction with other buffs and debuffs (such as Well of Radiance and Tether), could lead to the game's biggest enemies being melted.

This is speculation, but until Bungie comes clean, all we can do is watch and enjoy; Bungie has yet to comment publicly on this supposed glitch for now, but they are definitely aware:

While this is a major bug (bug it has to be, right?) ), it's not game-breaking, so it's possible that Bungie will let people enjoy it for a while before it's fixed; I've contacted Bungie, and will update when I hear back.