Tested the arena made of just 2 points, usually it is made of 4 points to make the rectangles yes, there's one attack that consists of making the arena 6 points and oscillate them to showcase the feature, but yeah you can define the polygonal arena with just 2 points if you so desire for whatever the reason is.

One thing I probably didn't mention is that the order in which you define a shape with the points does matter, define the points of your shapes counter clockwise, if you do it inverse... well nothing will change aside from the borders of the box being inverted, this means 5 pixels worth of sprite and therefor collision as well, will be inside the box, and unless you were doing precise calculations on the space available inside the box, well you probably don't care about this much, btu still just a heads up, everything else should work fine.

Yeah that's pretty much it, more work, more testing, more documenting, stay tuned!