In the "[Tutorial] How to Make a RimWorld Mod, Step by Step" topic it is referenced "- Next we want to reference the original Projectile code, so we can write a new impact event." , but where can I find said code? Does it come with Zhentar's ILSpy Mono ?
Zhentar's build of ILSpy is a tool used to look into the contents of RimWorld's .dlls, specifically Assembly-CSharp.dll. This is where all the game code is located (you can also look into the unity engine dlls which RimWorld is built on with this). Certain tools can also decompile these .dlls (MonoDevelop does a decent job), but Zhentar's ILSpy sucessfully decompiles the yield/return blocks used for a range of purposes in RimWorld, which other decompiler tools do not.