[Penguin]

Bring back the minigames world, with regular (maybe monthly) tournaments or competitions. Get people to log in at the same time and have fun in team ctf, spleef, or just a parkour map where the winner gets some sort of prize

Plugins. Chess, marriage, mpet, vehicles. Of course, this is always dependant on whether the plugins have updated to the newest version of minecraft or not

Build competitions in creative where people compete to build the best parkour / minigame / shop / spawn build, and the winner has their build actually used in the server for its intended purpose

Perhaps, a dedicated team for setting up minigames? I really love minigames okay.

Fun activities like treasure hunts, mazes, puzzles, and the likes that people can participate in. Maybe a quiz that people can enter just by talking in chat?

"Help a guest" activity where everyone forms a team and helps a new player get set up with a simple house? After all, most people on the server enjoy helping others.

Team builds. Pick something awesome to build and get people together to build it over a period of a few hours.

End dragon fights!

Elytra flying!

I ran out of ideas...