The real Terraria code isn't much better. Here's their 3MB [decompiled] NPC.cs: https://raw.githubusercontent.com/csnxs/Terraria/67de21a27e1... They had serious problems implementing multiplayer because they had to synchronize objects with 50KB of state every frame.
HitEffect is a quite the function.
This reminds me of working on CDDA[1] before many of the refactors hit.
CDDA is an interesting case, it stemmed from a situation similar to the original post (one person project, embarked upon it before knowing how to do so). It was a complete mess of macros, spaghetti code and data and code living happily side by side.