@BabciaRosie I will make full character challenge guides for all characters, on this forum, from next month and onwards, for people who need help completing them. That's totally fine! 🙂
For Space Cadet, I also needed vanquish assists. I play on Xbox and on split-screen, so we help each other getting assists on heroes by the person trying to get the assists get one or two low-damage shots on the hero that we're targeting and the other player gets the vanquish to give the first person the assist, and rinse and repeat. You could try doing this in PvE, or Ops, use your pots or bots to do most of the damage. In PvP, try and simply shoot at everyone a few times each and hope that your teammates can earn you assists.
It's most likely that the reason that this challenge is implemented for Acorn and Space Cadet is because the game wants you to team up with Oaks and Space Stations as a passenger and get assists that way, so you could try that in PvP if they are Oaks or Space Stations present on your team, or in PvE with a friend or in split-screen.
These strategies can also apply to the Acorn/Oak, try to do low damage to each enemy when there are allies around you to get that vanquish for you! 😃
Hope that helps you out! 👍
Regards
@TheSprinter85