http://breezewiki.catsarchywsyuss6jdxlypsw5dc7owd5u5tr6bujxb7o6xw2hipqehyd.onion/crosscode/wiki/Arena
The arena has many Cups, which can be unlocked by default or by completing specific parts of the main game. Each cup consists of one or more Rounds. In a round, you must fight and defeat specific enemies, which often spawn in two waves. The rounds can be taken on individually, although it is necessary to complete each round in order to unlock the next one.