Cycript is a tool I find very helpful. It's an effective REPL for Objective-C. When I updated to macOS Mojave, I found that cycript no longer worked because it was linked against an old version of Ruby. After attempting to compile from source, I tried another solution. install_name_tool is an open source tool for modifying the names of linked shared libraries in a Mach-O.
$ install_name_tool -change /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/libruby.2.0.0.dylib /System/Library/Frameworks/Ruby.framework/Versions/Current/usr/lib/libruby.dylib Cycript.lib/cycript-apl
$ install_name_tool -change /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/libruby.2.0.0.dylib /System/Library/Frameworks/Ruby.framework/Versions/Current/usr/lib/libruby.dylib Cycript.lib/libcycript.dylib