As part of the Destiny 2 Invitations of the Nine (opens in new tab), you'll need to visit Io to kill Cabal, Taken, and Vex for the Magician bounty. You also need to clear the Pyramidion Strike. Sounds easy, right? Well, the thing is, Cabal aren't exactly running all over the place on Io, and unfortunately Bungie's patched the bug that allowed players to progress Invitations and earn samples by killing enemies anywhere in the game. This means getting Cabal kills is handily the most time-consuming part of this bounty, but don't worry, it's not impossible.
Here's the good news: Cabal do in fact dwell on Io. They don't roam around much, but hordes of them will spawn in during the Cabal drill Public Event which appears in the Rupture and the Lost Oasis. Be sure to extend your Public Events by triggering the Heroic version; shoot the three cooling vents on the sides of the drill until they start smoking. This will cause more Cabal to spawn at the end, which means more kills for you. You can drag things out further by leaving the Cabal boss alive for as long as possible. Remember, you're here to get Cabal kills, not to clear the event.
These events can be few and far between, though, so this is probably going to take a while. Unlike with most other Invitations, you can't speed up the grind by running Lost Sectors or Adventures, because sadly the Io quests don't feature many - or indeed any - Cabal. As you may have noticed, it's mostly just Taken and Vex. That said, you can at least talk to Asher Mir and grab some planetary bounties to make this process more profitable and less painful.
Here's everything you need to know about the loot and balance changes in the latest Destiny 2 patch notes (opens in new tab).