Download Crazy Client
Then rename it to AssembleeGameClientProxy.swf
https://image.ibb.co/j3SCGx/rename.png
And then put it in where ROTMG steam is download either in C: or in D: \Steam\steamapps\common\Realm of the Mad God
https://image.ibb.co/gSug9H/replace.png
When thats done open the game in steam, then it will automatically log in your account on steam.
Have Fun bobo bobo bobo