Do everything you can using 3d entities and simply limit their movement to 2 axis. Blitz3d's commands are better and will give you more possiblities this way - you can tweak the camera to kill any perspective if you wish, though a little 3d perspective in a 2d game can work really well...and to top it all off you can use anything from the code-archives that might be handy with next to no modification where entities are concerned.
I'm doing exactly the above for a 2d platformer.
I'm doing exactly the above for a 2d platformer.