Pandora Behavior Engine is a specialized software program designed to patch the behavior files in Skyrim Special Edition, specifically those in the Havok 2010 .hkx format.

Built on the knowledge of dedicated modders and programmers, this tool enables Skyrim modders to create a better gameplay experience by patching and optimizing behavior files for humans and creatures within the game.

Havok Behavior is a proprietary middleware software for controlling animation logic in video games through non-deterministic finite state automata. These automata are serialized in pack files with the hkx extension using a custom binary format, which hkxcmd and hkx2 can unpack.

Thanks to the work of modders, these pack files can be edited using various tools, the most prominent being Zartar's Behaviour Tool and Haviour.

A behaviour patcher is a program that reads the edits to the various pack files and merges the edits into a final output. This is necessary to have multiple mods making edits to the same files without conflicts.

First pioneered by Fore through FNIS for Skyrim, then further developed through Nemesis, Pandora is the latest culmination of the decade of work that has gone into the relatively underrecognized field of behaviour.

	Pandora	Nemesis	FNIS
OS	Windows/Linux/MacOS	Windows/Linux	Windows
Game	Skyrim SE/AE	Skyrim SE/AE	Skyrim SE/AE/LE
Support	Humans & creatures	Humans & some creatures	Humans & creatures
Patching	Behavior, Imperative	Behavior, Imperative	Behavior, Declarative
Export	HKX2E	HKXCMD	HKXCMD
Cross-Compatibility	Most FNIS mods & all Nemesis mods*	Almost all FNIS Mods	Own Format Only
Source	Open Source (GPL v3)	Open Source (GPL v3)	Closed Source
Animations	Add via behavior or animlist	Add via behavior or animlist	Add via animlist

*Pandora does not support FNIS/Nemesis features for which a modern alternative exists, e.g Sexy Move, PCEA replaced by OAR and baked motion data obsolete by AMR