I've gotten quite a bit of my game engine implemented now, and while it's about 70% complete, I'm currently working on some other aspects my old one did not address in detail.
The RPG Maker engine is a 2D affair in which movement is handled on an X/Y plane, and while diagonal movement is supported (using both stock game sprites and 8 directional sprites), the game renders this in an X/Y fashion, meaning it can present issues when working with events, as these ordinarily do not take anything other than the stock 4 cardinal directions (up, down, left, right) into account, and then only on a 32 x 32 pixel range on a X/Y grid.
This means I am currently attempting to make sure events work well when approached from all eight directions and that this results in no graphical weirdness with overlays and other effects.
Another thing I'm working on is attempting to make sure there is rudimentary mouse support. The engine comes with basic gamepad support, but mouse control is not ordinarily supported, and I have to make sure that it not only works, but that it also doesn't cause input issues with using the keyboard or gamepads.