Raven Software licensed the Doom engine from id Software to create Heretic, a medieval-fantasy-themed FPS released in 1994.The Serpent Riders, three powerful evil beings, have enslaved the seven human kings and turned their subjects into their puppets. The Sidhe Elves, of which the player character Corvus is a member, remain unaffected by the Serpent Riders' magic powers and are declared Heretics, to be wiped off the face of the earth. The Sidhe respond by extinguishing magical candles that weaken the seven kings' armies but also the Sidhe themselves. The Serpent Riders opportunistically destroy the Sidhe elders and force the rest of them into hiding.Your task as Corvus is to seek out the weakest of the three Serpent Riders, D'Sparil, and destroy him. The other two serpent riders, Korax and Eidolon, would later be destroyed in the game's sequels, Hexen and Hexen II.The gameplay differs from Doom seemingly only in setting (medieval fantasy vs. futuristic military/hell). The levels follow the same formula of "get yellow key to open door to green key which opens door to blue key which leads to exit." The original order-by-mail full game consists of three episodes of eight normal and one secret level, with two more added in a licensed retail version (Heretic: Shadow of the Serpent Riders) vis-a-vis The Ultimate Doom.The weapons seem to be medieval fantasy-themed edits of Doom's arsenal: An Elven Wand for the pistol, the Ethereal Crossbow for the shotgun, the Dragon Claw for the chaingun, the Phoenix Rod for the rocket launcher, the Hellstaff for the plasma rifle, and lightning-shooting Gauntlets of the Necromancer for the chainsaw. There is no direct equivalent to the BFG, and the player is instead offered the rapid-firing Firemace (which fires bouncing metal spheres, which, when using a Tome of Power, can kill most enemies in one shot).One notable addition was the inventory system, which allowed the player to carry items to be used later at will. Among these are the health-pack Quartz Flask and Mystic Urn; hourglass-shaped Time Bomb of the Ancients; a simple Torch; the Tome of Power, which gives your weapons new and more powerful attacks for a limited time; and a magical egg, Morph Ovum, that turns any enemy it hits into a chicken.Heretic also upgrades Doom's "2.5D" engine to nearly-3D: the game allows you to look up and down - and failing to do so when attacking an enemy above or below your level means your shot will miss, unlike in Doom where all interactions are really done in 2D. A powerup also enables the player to fly for a limited time. It's still not possible to create a room above another room, or objects like ledges or bridges that can be passed over and under.Enemies included flying red gargoyles, golems, undead warriors, ophidians, disciples of D'Sparil, and were-dragons, each with melee and ranged attacks of varying power, and the melee-only Sabreclaws. Similar to Doom's use of Barons of Hell as bosses for one episode and then sub-bosses later on, the giant floating skull-like Iron Liches populate the later episodes. Standing in for the Cyberdemon are the Maulotaurs, giant minotaurs with fireball-slinging hammers.The game spawned three sequels:
Hexen (1996) - The player plays as one of three character classes to hunt down the second Serpent Rider, Korax.
Hexen II (1997) - Uses the Quake engine, unlike the Doom engine of its predecessors. Four different character classes hunt down the third and final Serpent Rider, Eidolon.
Heretic II (1998) - Based on a modified Quake II engine. Unlike the previous games, uses a third-person view. The protagonist from the first game, Corvus, must stop a mysterious plague that has decimated his homeland.
Bag of Spilling: Aside from the "lose all your weapons between episodes" shtick that was pretty common back in the day, Heretic also let you only carry one of each inventory item to the next level, except for the Wings of Wrath which you just plain lost. On the other hand, this means you're encouraged to use your items as you get them, thereby averting Too Awesome to Use.
Baleful Polymorph: The Morph Ovum, Porkelator and Seal of the Ovinomancer items in the first three games of the series.
In the multiplayer for Heretic II, the Morph Ovum can be used on players. Using the Tome of Power after you've been turned into a chicken will turn you into a giant chicken. This doesn't work in Heretic I.
Big Bad: D'Sparil, the first of the Serpent Riders.
Cherry Tapping: Heretic II lets you use Morph Ovum against other players in multiplayer, but a good player can still get in your face and peck you apart even then. Helped by the chicken form being small and hard to hit.
Damage-Sponge Boss: Maulotaurs are fairly easy to avoid if you have enough space to move around in. However, they have an absolutely obscene amount of health, and you can deplete much of your ammo reserves just taking down one of them if you don't use a Tome of Power.
Degraded Boss: Iron Liches and Maulotaurs are met in regular gameplay after their boss introduction. So after Episode 3 (Where you fought D'Sparil), bosses are large groups of them.
Descending Ceiling: A frequent trap. Like Doom, instead of being caught in a room with a descending ceiling, there's crushing traps lining certain walls or rooms.
Difficulty Spike: The two episodes added in Shadow of the Serpent Riders ramp up the difficulty. E4M1 alone has a Maulotaur and a whole posse of Iron Liches, and not a lot of weapons or ammo to go around. Later levels have at least two Maulotaurs and five Iron Liches, sometimes all nearby each other.
Episode 1 isn't much to write home about difficulty wise, until you get to the Citadel, which throws hordes of enemies at you from every direction (with lots and lots of Gargoyles sneaking up on you.)
Episode three has this to a lesser extent, with at least one Iron Lich per level on the higher difficulty settings, but that's still a lot more manageable than the new episodes.
Dual Boss: On the easier skill, the Iron Liches and Maulotaurs are the bosses of the first two episodes. If you increase the difficulty, they appear in a pair or triplet.
In the expansion Shadow of the Serpent Riders, the episode's final level has at least 8 of these bosses on the hardest difficulty.
Dying Curse: D'Sparil utters one upon his death at the end of the original Heretic. It turns out to be the reason for the following two episodes in Shadow of the Serpent Riders, and its full effect is seen at the beginning of Heretic II''.
Flunky Boss: One of the main things that distinguishes D'Sparil from Korax and Eidolon is that he constantly teleports away while summoning mooks to help him, instead of just straight up trying to tank you like the later Serpent Riders do. Korax does this to a lesser degree, where he only teleports away once and opens doors to Monster Closets, but D'Sparil is much more annoying in this regard.
Gorn: Some attempts in the manual, and enemies do tend to die messily in the game as well.
Harder Than Hard: Black Plague Possesseth Thee difficulty level makes enemies way faster.
Healing Potion: Crystal vials, quartz flasks, mystic urns. The latter two you can carry with you.
Hellgate: E1M8 and Episode 2 are both named "Hell's Maw".
Last of His Kind: Corvus isn't quite the last of his kind, but the remaining Sidhe elves have all gone into hiding.
Lethal Joke Item: The Fire Mace is a weird short-ranged "machine gun" that is completely ineffective against ghost monsters, and against most monsters, isn't any better than using the Hell Staff (Plasma gun). Also, if the floor texture is water, the shots will sink. However, if you power it up, then it shoots bigger, slower spheres that will One-Hit Kill anything excluding boss monsters. Oh, and the big spheres travel through teleport pads. It still will not hit ghosts however.
Level-Map Display: In tan and sepia, to look like an ancient scroll. There's also a map scroll that reveals the entire map.
Another name for a sledgehammer is a "maul", hence the Maulotaur. This may also qualify as a Punny Name.
Mondegreen: The Disciples of D'Sparil seem to alternate between saying "He's steppin' out Yoshi" and another phrase which sounds slightly rude; D'Sparil himself appears to say "I've seen Mr. Davros". All of these are actually English phrases reversed.
Non-Indicative Name: E4M6 is "Halls of the Apostate" — rather strange, given that you (the player) are the Heretic and hence the Apostate, and any halls you might have are either millions of miles away on another planet, or in another dimension.
No Sell: D'Sparil can teleport at will and likes to do so just before your shots hit him. Plus, he and the Maulotaurs take greatly reduced damage from normally BFG-caliber weapons like the powered-up Hellstaff and Firemace, and are unaffected by splash damage.
One-Man Army: Corvus marches through hordes of D'Sparil's minions, through hell and back to get at D'Sparil, and then through the rest of D'sparil's army trying to find his way home.
Power-Up Letdown: Like Doom, the Shadowsphere causes enemies to fire shots wildly. While useful if you stand still, it actually makes projectiles harder to dodge, especially in large groups. One advantage it does have is that certain physical attacks (Like the undead warrior's axes) will pass right through you.
Puzzle Boss: The final boss of Heretic II can only be temporarily defeated through use of force. But if you don't execute a certain action in the room in the very small window of time he's down, he'll get back up, regenerate his health back to 100% and you'll get to fight him all over again.
Retcon: The protagonist of Heretic was unnamed until Heretic II, which also established that there were a total of seven true Tomes of Power in existence, (At least, his existence, since they reappear in Hexen II) and that Corvus really had only one of them. The ones he picked up in much larger quantities in his first adventures were fake tomes.
Shareware: Much like doom, the first episode was shareware.
Shock and Awe: The Gauntlets of the Necromancer shoot Green lightning. Powered up, the lightning is red and steals life.
Shout-Out: The second difficulty level is a reference to Toys-R-Us.
Standard FPS Guns: Even if the weapons are shown as magical staffs, and artifacts, many of them still seem familiar if one has played Doom. (Shown in terms of WITHOUT / WITH "tome of power" respectively.)
Took a Level in Badass: Corvus' quarterstaff in the original was the worst weapon you had. Lousy damage, short range, plenty of retaliation time for bad guys, can't harm ghosts at all and any other weapon is better with the Tome of Power. In Heretic II, a blade is added to one end and it becomes one of the coolest weapons in the game that can dismember humanoids to make them harmless, execute spinning attacks or mid-air downward stabs to do increased damage and (with the help of shrines that give permanent upgrades in power) remains a potent weapon throughout the game.
Tornado Move: The monsters known as Iron Liches can create tornadoes to attack you. The tornadoes sweep you up into the air and do a great deal of damage besides.
In Heretic II, a powerup finally allows leaving a tornado countermeasure, also in Hexen II the Crusader's third weapon can create tornadoes with the aid of the Tome of Power.