I spent some time this weekend researching some details about FE3’s arena.
Specifically, I wanted to see how it selects opponents and if it’s possible to predict who you’ll fight.
It turns out that sometimes it is, sometimes it isn’t. This more or less lines up with my experience playing without this info.
Each class has an associated table of possible enemy classes, and the arena uses one of 256 possible random values to select a class from the table + the enemy’s level. (Note: there are not 256 possible enemy classes, usually it’s more like 8).
Since the arena reward is calculated based on the selected class and the enemy’s level, it’s possible to narrow down the list of possible opponents. Sometimes it’s possible to narrow it to a single class, though not always.
I made a Github Page which has some more details, as well as tools to help predicting fights. Hopefully this is useful to some people.