The Aridara Arena is part of the Pyramid of Prophecy Expansion which came out in spring 2019, to the roguelike game Heroes of Hammerwatch (released March 1 in 2018, developed by Crackshell, and distributed by Devolver Digital).
The arena was a new game mode where the player (or players) could fight waves of increasingly difficult enemies while dodging different traps and at the same time trying to keep the crowd pleased, as a happy crowd will throw items and potions to you. It's more of an arcade experience than the rest of the game, where you can test your different characters' mettle between runs of the normal game.
You can watch a video (not made by me), linked here, that shows the arena and a bit how it works.
I worked for a couple of months on the level design of this part of the expansion during the summer of 2018. This was equal parts designing a large amount of different setups of traps and layouts of the arena; and scripting different enemy behaviors and testing different wave formats for their appearance.
Since what I did was more or less the first work that was ever done on this part of the game in the Hammerwatch game engine, most of what I did has been revised or has evolved into new things along the development, so there are really few specific features that I might actually take credit for. However, some of the larger arena shapes and concepts seems to be unaltered still.