Build a Level editor
The level editor is a key target of game development.
AC has emphasized that J Blow emphasizes the level editor as core to his games.
share the level design
The rest of the team can contribute
feedback loops
The editor/designer must be able to play-test their design quickly, rapidly
(for games of a certain size)
It's likely there are games, especially early on, that don't get a level editor at all - it may not make sense to have one.
Backlinks
Game AI can be modeled with behavior trees.
We want a very expressive behavior tree lib, so we can be expressive in our AI design.
Ideally Behavior Trees can be visualized and debugged easily.
Enemy AI design, Level Design. It's all coming together.
Somewhat related: Build a Level editor
See also: Goal-Oriented Action Planning (GOAP)