DevilutionX is a modern C++ source port of the 1996 action role-playing game Diablo and its Hellfire expansion. It is a monolithic game engine that reimplements the original game's logic, rendering, audio, and networking from scratch, requiring the original game data files (DIABDAT.MPQ or spawn.mpq) to run. The architecture is highly cross-platform, targeting modern desktops (Windows, Linux, macOS), consoles (PS4, PS5, Switch, Xbox, Vita, 3DS), retro platforms (Amiga, DOS), and embedded devices (Miyoo Mini, OpenDingux), all managed through a sophisticated CMake build system. The codebase is data-driven, loading game content (monsters, items, spells, levels) from tab-separated value (TSV) files and original MPQ archives. It features a robust Lua scripting engine for modding, a comprehensive input abstraction layer supporting keyboard, mouse, gamepad, and touch, and a modular networking stack supporting TCP and ZeroTier P2P multiplayer. The project maintains an extensive test suite using GoogleTest and GoogleBenchmark, including deterministic dungeon generation tests and performance benchmarks. While the codebase exhibits tight coupling inherent to game engine development and carries significant platform-specific conditional compilation (#ifdef sprawl), it contains several high-quality, isolated utility components that are safely reusable. These include a robust INI parser, a fixed-capacity static vector, endian-safe I/O helpers, an A* pathfinding implementation, and a KD-tree for color quantization. The code is written in modern C++ (C++17/20 style) with pervasive use of std::expected for error handling, demonstrating strong engineering practices despite the complexity of its domain.