Design
I was thinking it could be set in an infinite void of purple. The platform the players would fight on would be an about Ice Breaker size circle of prisms or fragments (Like in Marvel movies) with a wall on the bottom of the map the players can climb up, like in Castleween. Also like Ice Breaker, four players each would spawn on either side of the centre point
Mechanics
The Shrinking Circle could be a merging of Castleween and Ice Breaker (find it really funny how the shrinking circle is basically the only two maps I've taken inspiration from.) The map will slowly break apart, this would be sped up by players running around and landing on it. But unlike Ice Breaker, when a piece comes apart, it remains for about ten seconds before dissipating into the void.
For weapon spawning, I was thinking a fun idea could be for rifts to other maps could open (Out of the players reach, obviously) and drop weapons from them before closing. If this wouldn't work out, just the rifts spawning around as an Easter egg could also be cool, in this case, weapons would spawn similar to how they spawn in Ice Breaker.
For a map exclusive mechanic, portals to other parts of the map could randomly open that the players can jump through and stuff. I feel like this would offer multiple gameplay opportunities in this map and future maps. It could also just be really funny, which I would say is even better. To prevent camping, I would say that if someone is clinging to the wall for too long, a portal to the centre of the map (or around that point) will spawn beneath them, and once they go through it, it disappears.
Weapons
All types of weapons are supported. As for new weapons, I was thinking maybe a grappling or harpoon gun that pulls players it hits towards you or pulls you to where it hits (really depends which one we go for.) In conjunction with the portals, this could be really funny, just shooting through a portal and pulling someone out from the other side just sounds hilarious to me.
Gameplay
I expect this to be similar to Ice Breaker, with no sliding. Everyone running around throwing each other off the map, but also being cautious as to not cause the map to break apart quicker. But I would expect them to just be silly with the portals. Like throwing a bomb through or just running around them like in a cartoon. Players can obviously die by being thrown off the edge, though they can recover from this by climbing the wall back up. Either way, I believe players would have lots of fun on this map.
Anyway, that was my idea. Thanks for reading, I hope you all see my vision and consider it for winning the competition. Also I do just want to clarify that I did edit this post, but only to add more details I failed to add before. I hope you understand.