Into the Breach on OS X with Wine

Requirements

That's right. You only need to download Wineskin.

Instructions

  • Download and install Wineskin
  • Run Wineskin, download the latest engine (I've used WS9Wine2.22)
  • Select "Create New Blank Wrapper"
  • When it finishes creating the wrapper, right click on the wrapper icon and select "Show Contents"
  • Double click on Wineskin (note: this is the Wineskin configuration tool; it's different from the "main" Wineskin Winery executable)
  • Select "Advanced", "Tools", "Winetricks"
  • Search "steam" and install it
  • When it finishes installing Steam, click "Test Run" in the "Tools" window of Wineskin
  • Let Steam complete its installation by downloading all the updates
  • Exit Steam when the update is completed; do not run Steam after the installation is completed.
  • Go back to Finder, go to the window containing your wrapper (i.e. the directory that contains the Wineskin configuration tool); double click on your wrapper to launch it.
  • Log In into Steam
  • Install Into the Breach
  • Enjoy :)

Or check this more detailed guide on reddit.