I happened to stumble across a Japanese youtuber playing this interesting little flash game where you have to swap around characters to form 四字熟語, so after looking it up and trying it out I thought I would share it:
http://www.gamedesign.jp/flash/yojifla/yojifla.html
Be warned, it’s incredibly difficult since it’s designed to challenge native Japanese. There are 7 stages in total and I’m struggling to even get past the first one. There’s also an easier version where you make words of only 3 characters instead of 4: