SharpClipboard
C# Clipboard Monitor
Not original code, all credit goes here: https://gist.github.com/glombard/79863174. I added some additional functionality and got it working with Cobalt Strike's execute-assembly.
Blogpost
https://grumpy-sec.blogspot.com/2018/12/i-csharp-your-clipboard-contents.html
References
https://stackoverflow.com/questions/621577/clipboard-event-c-sharp
https://stackoverflow.com/questions/17762037/error-while-trying-to-copy-string-to-clipboard
https://docs.microsoft.com/en-us/windows/desktop/dataxchg/wm-clipboardupdate