One of the demonic sounds that the enemy Dark Bishop sometimes utters, when played backwards, actually sounds like his name.
The first place in the game where the Porkalator artifact can be found is on Hub 2: "Caves of Circe". Circe was a character in Greek mythology, who transformed Odysseus' crew into pigs.
The final boss of Serious Sam: The Second Encounter, Mordekai The Summoner, carries a staff very similar to the Bloodscourge, the last weapon of the Mage class in Hexen: Beyond Heretic. It should also be noted that the enemy as a whole looks very similar to D'Sparil, the final boss of Heretic.
The Steam download version of the game is listed as Windows 2000/XP/Vista platform because the executables are modified to use a DOSBox variant (v 0.70); additionally the traditional setup.exe is missing.
It is confirmed that neither Valve or id Software contacted the DOSBox project staff and initially the game didn't includes the TXT files that must be present under the GPL license (so they failed to fulfill 2 points of the GPL license).
Two days after the launch, there was an update that includes COPYING, AUTHORS and THANKS.txt of the DOSBox 0.71.
The villain's name, Korax, is derived from the scientific name of the common raven: corvus corax. This is an intentional joke as the game was developed by Raven Software.
Hexen was the first game Raven software released for the Macintosh.
In German, "hexen" means "witches", or "casting a spell" when used as a verb. Moreover, the game has a Warlock skill level - a warlock (or "hexenmeister") is the male version of a witch.
The PlayStation version can be called notoriously evil for being one of the few games on the system to require one ENTIRE Memory Card (yes, all 15 blocks worth) to save just ONE save game!
In the first HUB, "The Seven Portals" there is a secret level hidden. Once you're in it, you can find D'Sparil's (from the original Heretic) heart in there.
In the Necropolis, you can find graves that have the names of some of the authors written on them.