I'm all for cooperative missions but unfortunately, you're forced to go into voice chat as you have to call out symbols so it's not as simple as watching a walkthrough video and queuing up in LFG. It's also a fairly long mission on a timer as well so there's a good chance that if you screw something up or die, your teammate is gonna ghost out and look for another group. I'd just wait for the next Halloween event and hope it's available again.