This question can be asked on your perceptive view.
Having something to do in a lobby should be fun and engaging to players include things like “minigames, obby’s, arena” and more. This does depend on what game you are trying to make add things that fit the theme and style you’re approaching.
Placing common objects like leaderboards, obstacles, buildings, hidden areas, something that they could do and interact with each other, meaning players or friends small obstacle courses in the lobby allow players to explore the map so that players won’t get bored waiting for the intermission to start.
Add enough ideas in your lobby to keep players engaged and worth playing your game. It’s good to look at other games to get small ideas even think of some and go from there.
The game sounds like it’s derpy, and it’ll have custom physics much like Floppy Fighters so something where the player can experience the custom physics. You’ll want the lobby to be low poly and also be very bright and colorful. Just, when making a lobby, minimize the part count for lag and make sure it’s very easy to navigate and there’s lots of places you can move around in.
I suggest you to adding different details to your lobby even places far from the lobby, decorate the map in a way so not only the lobby is full of things but also places far from the map are also decorated, for example you could add some buildings and some billboards which advertise your game, some mountains in the distance. also you could add architectures from around the world.