Good questions. RAIN isn’t really built for 2D. We’ve been wanting to add 2D support for some time, but just haven’t been able to get to it yet. Here are some of the difficulties:
1) 2D usually uses a different coordinate system. RAIN is build on the standard Unity 3D coordinates and makes some assumptions there in a few places.
2) RAIN doesn’t recognize 2D geometry or colliders when doing things like generating navmeshes, raycasting, etc.
3) Although you could work around these issues, you will probably need to create your own Motor and Navigator to do so.
Things that should generally work regardless of 2D/3D:
1) AI Memory
2) AI Behavior Tree
3) Entities/Aspects/Sensors that don’t do raycasting and use radius detection only.
4) Mecanim support
5) Audio support
6) Custom AI elements
On the one hand, it isn’t terribly difficult to write a 2D motor and navigator - much simpler than the 3D case - but on the other hand it does require some knowledge of RAIN. You are also free to use the HeuristicSearch class for your A* pathfinding.
If you decide to use RAIN, reach out to us directly (email@example.com) when you have questions/issues.