So I watched a minecraft tech series where around 20 people played on and every once and awhile they had an event that was usually a parkour or maze with chests and good stuff all around it and in the end. What made this event so cool was that the event area was fucking massive, like 500 blocks by 500 blocks, so all the teams were able to bring bombs and plasma guns and random shit. I think adding this type of concept with minimal restrictions (like no antimatter or nukes or something SUPER op), and this will give new guys more incentive to work together.
Just to add on, I think a huge parkour event wouldnt really work because most guys can fly, so one idea I had was to have essentially a race, 100 blocks wide and 1000 blocks long so in addition to trying to get to the end you can bring missiles and stuff to stop other people, obviously there needs to be a lot of restrictions but just an idea.