He is the first and the youngest of the trio of Serpent Riders, using cunning and deception to initially gain dominance of Parthoris, the world of Heretic. He declared the supernatural race of the Sidhe to be forever hunted as heretics to their new Order. The Raven sequel, Heretic II, begins with D'Sparil's death and shows D'Sparil cursing Corvus.
The name "D'Sparil" almost certainly comes from one of id Software's earliest games, The Catacomb (1990); level 12 of this is called "The Tomb of Desparil".
The player, as Corvus, fights D'Sparil in a wide arena with a large trident-shaped ledge in the upper-middle, and various teleporter destinations scattered around the map. D'Sparil initially is seated upon a Green Chaos Serpent, which are prevalent in Hexen.
The Serpent is the most powerful of any Chaos Serpents in the series itself, able to belch fireballs, at first in single units, and then after falling below half its Health, shoot a line of three scattered fireballs at the player. The Serpent can also make a bursting charge of speed towards the player when stunned by attacks. Like the Iron Lich and the Maulotaur, D'Sparil is immune to the effects of the Morph Ovum and cannot be instantly killed by the Firemace under the influence of the Tome of Power. D'sparil also has a 50% immunity to the powered up Hellstaff's rain like the Maulotaur.
When the Serpent dies, D'Sparil will electrify and rise up, and start attacking the player. His abilities are a mix of offensive and defensive tactics, one being to fire a blue, trailing bolt of electricity for extreme damage to unarmored players. He can also shoot a pair of purple rings which turn into Disciples of D'Sparil, and teleport himself to one of the 6 raised platforms in the area. As he is damaged more, he will teleport more often. D'sparil will also often teleport when he is hit by a Phoenix Rod missile or Hell Staff rain (the game code does a specific check for these weapon hitting him).
When D'Sparil finally dies, his flesh and robes explode and burn away in a burst of electrical energy, leaving a clean, intact skeleton that falls to the ground. All the other enemies on the level will instantly die, and the portal to the end of the third episode will be revealed.
D'Sparil's entire fight is 5500 Hit Points; 2000 Hit points for the Chaos Serpent, and D'Sparil himself having another 3500 Hit Points.
First off, run all around the large arena, collecting everything you can, including the Wings of Wrath. Fly to the ledge above, there are plenty of Mace Spheres, as well as two secret doors, one on the far end of each side, containing a Mystic Urn and a Ring of Invincibility; at this point D'Sparil should rarely if ever even attack you until you start fighting him in earnest. Now pay attention to D'Sparil. Use the Phoenix Rod from a distance and you should be safe, but be aware that the Serpent will start to run and fire more fireballs the weaker it gets (by this point in the game, you should have no trouble circle strafing). When D'Sparil rises, his only attack is a fast lightning bolt that deals massive damage but gives you plenty of warning, but the real challenge comes from his teleporting around and summoning Disciples; you should eliminate him as quickly as possible since the Disciples he summons may annoy (or kill) you. The Hellstaff might be an option to kill him, but consider the Phoenix Rod as well - D'Sparil teleports rather often so slower projectiles from too far away and continuous attacks won't work so well. If you've got a Firemace, it won't be so hard for you, and if the Disciples he summons get out of hand, consider using a Tome of Power with the Dragon Claw to clear them out. Good luck.
If you are really having trouble defeating D'Sparil (as I was) this strategy might help. Despite multiple attempts to best him, whatever strategy or combination of weapons I used against him failed. The main problem is that when he was seriously low health, D'Sparil began teleporting almost instantly when I had a line of sight on him. This combined with the many minions he had sumonedd led me into defeat again and again. As mentioned above, D'Sparil has three powers at his command, he can attack directly, teleport away or summon Disciples of D'Sparil. However, although in a way two of these are defensive abilitess, he seems to only ever use them when he has line of sight to the player. Therefore when you defeat his first serpent riding form, then while he is rejuvinating himself, you can run into one of the narrow gaps in the raised Serpent Rider sigil (the structure you appear on top of at the start of the duel). Without a line of sight D'Sparil will come looking for you, appearing at the end of the narrow passage. At this point you obviously need to begin chipping down his health. He is rather hard to hit, because of the narrow walls. I used up my Phoenix Staff first, before using the accuracy of the Dragon Claw to whittle him down further. You have no room to dodgee, so you must force him to teleport away reasonably quickly, if D'Sparil gets a good angle he will kill you very quickly. I can't confirm this, but it seemed to me that if D'Sparil teleports before the full animation for his summoning spell is complete, then his disciples are not created. In any case, using this tactic he managed only to summon half a dozen disciples instead of the 60+ or so I was used to managing. Towards the end, when low on health D'Sparil will become virtually impossible to hit because as soon as he rounds the corner into line of sight of the player, he will teleport. When you reach this stage of the battle, you must go out to finish him off. I actually killed him with the wand, sniping him from range, and because he had so few disciples it was not a problem to avoid their magical attacks. The whole battle took around 30 minutes to fight this way, however, if like me, you lack the skill to beat him in the orthodox manner on the hardest difficulty, I can confirm this tactic works.
The demonic incantations of D'Sparil are actual phrases recorded backwards:
SORSIT - This sound is hard to understand, but some possible interpretations are "Now ravens shall chew your flesh" and "I will torture your flesh"