Usually the first you see of a darkstalker is the orange line of its flaming sword. Then its single red eye comes into view, and the sword illuminates the dark grey body and four arms. If it carries a cage, say your prayers.
The darkstalkers patrol massive cavern complexes underground. Those that only carry a flaming sword wordlessly threaten any intelligent creatures they discover, driving them away and maintaining a territory for their people. Those that also carry a small iron cage attack any intelligent creatures they encounter, trapping their souls in the cage and taking it deep underground. Nobody has ventured far enough into darkstalker territory to discover what they do with these souls.
Darstalkers fight with their magical flaming swords. They can also point the sword at a target and fire a thin line of flame. In addition, darkstalkers occasionally fire powerful beams of red light from their eyes. These are weird creatures!
Darkstalkers have no apparent sensory organs except for their glowing red eye. They do not speak, but they do appear to affect air pressure when attempting to communicate, using a sudden heavy air pressure to threaten others.
For stats, I'm going to base this off the CR 5 half-red dragon veteran, which has appropriate sword attacks, plus a fire breath attack that I'll change into an eye beam. I'll also swap out its heavy crossbow attack for a fire attack from the flaming sword. It'll get 60 feet of blindsight, too, since it lives underground.
OK, let's do this!
Homebrewery stat block:
Medium humanoid, unaligned
- Armor Class 18 (natural)
- Hit Points 65 (10d8 + 20)
- Speed 30 ft.
STR DEX CON INT WIS CHA 16 (+3) 13 (+1) 14 (+2) 10 (+0) 11 (+0) 6 (-2)
- Skills Perception +2
- Senses Blindsight 60 ft., Passive Perception 12
- Languages --
- Challenge 5 (1,800 XP)
Multiattack. The darkstalker makes two flaming sword attacks.
Flaming Sword. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit 8 (1d10 + 3) slashing damage.
Flame Strike. Ranged Weapon Attack: +3 to hit, range 100/400 ft., one target. Hit: 6 (1d10 + 1) piercing damage.
Eye Beam. The darkstalker sweeps a beam in a 15-foot cone. Each creature in that area must make a DC 15 Dexterity saving throw, taking 24 (7d6) radiant damage on a failed save, or half as much damage on a successful one.