you can mix discus, but its not easy and there are many factors its not something you should try when you first start out with discus.
I also dont think a clown knife would work well with them, I have seen a sliver arow done though.
they are well worth getting but sometimes mine piss me off, they are very very shy else you feed them otherwise they hide as soon as they see you for a good 10 minutes then come out and swim around. more of a sit in bed relax fish or a kitchen table room imho
