I’m debugging an Oracle package using PL/SQL developer, but I’m running into a problem – one of the parameters is a CLOB (it’s a big ass XML string). I can pass it in from the application side and have it be a CLOB, but in the PL/SQL debugger, I put the string representation of the XML into the debugger so the proc in the package treats it as a CLOB? As it stands, when set it, then step into the package, the parameter evaluates to NULL, but the string is fine.

you can always use the pl/sql block that is invoking the SP. In this case deselect the corresponding checkbox to the CLOB parameter, then replace the calling statement with this:
notice that the colon before myClob1 were removed.