Update: Multiple players have confirmed that while the secret Io mission doesn't reward Black Spindle, per se, completing it does get you a revamped version of the Exotic sniper called Whisper of the Worm. Destiny YouTuber Indica received what may be the world's first Whisper just minutes ago:
Just got Black Spindle! Video up in around 25minutes. pic.twitter.com/hPTdhvWpQKJuly 20, 2018
Twitch streamer gelatosquid and his fireteam received their own Whispers around the same time. Here's a clip of their victory, which also shows the mission's final room, which contains not one, but three Taken bosses:
It's unclear who achieved the world's first Whisper completion. Bungie will likely confirm the winner soon enough. One thing we do know is that Black Spindle is back. The Exotic perk on the Whisper of the Worm, White Nail, is exactly what players were hoping for: when you land three headshots rapidly, the gun's three-round magazine is refilled for free without using ammo from your reserves. It also has Mulligan, occasionally refunding missed shots.
Finally, YouTuber Datto has a complete rundown of how to obtain Whisper of the Worm:
Earlier today, Destiny 2 players found a secret, timed, 380-Power mission called "The Whisper," which is attached to a public event that occurs on Io. At the time of writing, nobody has finished the mission yet (or at least posted proof of it), so the reward for completing it is still a mystery. But given the nature of the mission—a timed, alternate challenge full of Taken—Destiny veterans are confident that it contains Black Spindle, an Exotic sniper rifle from Destiny 1 which was unlocked in a similar way.
You need to get a little lucky to trigger the mission. Go to Io and wait for public events to spawn. The mission can only be activated during the Taken blight public event. Other public events, like the Cabal lander, will not work. So, roll the dice and pray for Taken.
During the Taken blight event, a named Taken Knight will appear and, eventually, retreat to a cave. Kill him before he leaves and a portal will appear nearby. Activate the portal (or ask your fireteam leader to do so) to enter a lost sector which connects to a secret area via a hole found under a small blight. Here's a clip of streamer Slayerage watching an unlisted YouTube video showing where to find the blight:
The bulk of the secret area is a massive jump puzzle. Have a look at this video from YouTuber mignoneroy20 which shows a bit of the puzzle area:
Once you reach the end of the puzzle, you'll find several rooms crawling with Taken and blights. If the old Black Spindle mission is anything to go by, you need to kill all the enemies and blights in order to reach a final boss who you'll also need to kill—all within the mission's 20-minute time limit. But what comes next remains to be seen. I've heard whispers of some Vex interference, but it's anyone's guess at this point.
Our crack team of Destiny 2 experts (that is to say, Tim) is working on The Whisper now, and so is every Destiny 2 streamer and their dog, so we should get some answers soon. We'll update this story as it unfolds.