When I was creating artwork for my Undead Stock Art Bundle, I illustrated the above nasty, which I was sure John Stater had included in an issue of his excellent zine Nod..,and it turns out it was from the very first issue, currently available from Lulu.com (use the codes ONEFIVE for 15% off and ONESHIP for free shipping).
With his permission, the creatures (one of many listings in that book):
Headless screamers arise from the corpses of the beheaded. They are cruel and chaotic beings who delight in tormenting the living. Headless screamers look something like zombies with a noticeable red slash across its neck. They can throw their heads with alarming accuracy, and in fact do not need to throw their own head, for the headless screamer’s intelligence and animating force are in the body. Many of these creatures keep four or five heads handy. Thrown heads have a range increment of 20’. The thrown head will snap its jaws, dealing 1d8 points of damage to anyone hit and then latching on if the target fails a saving throw. A latched head inflicts 1d4 points of bite damage each round until removed. Headless screamers can telekinetically retrieve these heads and still move or attack each round. Headless screamers can also emit a shrill shriek from the air hole in their necks. Anyone hearing this must succeed at a saving throw or suffer a ‐1 penalty to hit, damage and save for 1 hour.
- Headless Screamer: HD 4; AC 3 ; Atk 1 claw (1d6) or 1 thrown
head (1d8); Move 15; Save 13; CL/XP 7/600; Special: Throw and
retrieve head, scream, immune to cold.
I GURPSified this as follows:
Headless Screamers (DF)
ST: 14 HP: 18 Speed: 5.00
DX: 9 Will: 8 Move: 4
IQ: 8 PER: 9
HT: 12 FP: 12 SM: 0
Dodge: 8 Parry: 9 (Unarmed) DR: 0
Throw Head (14): 1d crushing plus follow-up bite for 1d crushing
Bite/Punch (12): 1d crushing.
Scream: affects all hearing as Fear spell
Traits: Bad Smell; Bloodlust, Cannot Learn; Darkvision, Doesn’t Breathe;Doesn’t Sleep; Fragile (Unnatural); High Pain Threshold; Immunity(All mind control); Immunity to Metabolic Hazards; Intolerance: Living; Indomitable; Injury Resistance 1(cold); Injury Tolerance (No Blood, No Head, Unliving); Returning weapon (head: costs 1 FP); Sadism, Temperature Tolerance 10 (-115° to 60°); Unfazeable; Unhealing (Total). Affected by pentagram, True Faith, and spells that affect evil
Skills: Brawling-12; Wrestling-12 (+2 ST when grappling) Throwing-14.
Notes: Headless Screamers are truly evil, and cannot be negotiated with. They appear as normal zombies with obvious throat wounds. They can see even without heads, and usually keep 4-5 heads handy for throwing or wearing; Heads have range 7/14, and can return telekinetically to their hand.
GURPS DF stats are as follows (a blend of the Owl and Cat familiars from DF 5-Allies):
ST: 3 [-70] HP: 9  Speed: 6.00 
DX: 12 * Will: 12  Move (Air): 12/24 
IQ: 10  Per: 12  Move (Ground): 2 [-20]
HT: 12  FP: 12  SM: -3
Dodge: 9 Parry: n/a DR: 0
Bite or Claw (16): 1d-5 cutting.
Combat Reflexes ; Enhanced Move 1 (Air) ; Flight (Winged, -25%) ; Night Vision 8 ; Silence 2 ;Teeth (Sharp) ; Vibration Sense (Air) .
Disadvantages: Familiar [-22]; Laziness [-10]; No Fine Manipulators [-30] Curious [-1].
Skills: Aerobatics (H) DX-1 -11; Brawling (E) DX+2 -14; Flight (A) HT+1 -13; Observation (A) Per+1 -13; Stealth (a) DX+2  14† Survival(Woodlands) (A) Per+1 -13.
* Cost reduced for No Fine Manipulators (-40%).
† Includes +2 for Silence
Masters of an Meowl familiar can buy Common Sense (GBF,
-40%) ; Combat Reflexes (GBF,-40%) ;
Flight (Controlled Gliding, -45%, GBF, -40%) ; ];
Luck (GBF, -40%)Night Vision 3 (GBF, -40%) , 5 , or 8 , or Dark Vision
(GBF, -40%)  and Silence 1 (GBF, -40%)  or 2 .
Those who buy Flight can also add Enhanced Move (Air; GBF,
-40%) [12/level], but only to reduce deceleration.
At some point I have to write up my view of witches for DF. In the meantime, I have finished up some illustrations for Gabor Lux, hopefully Castle Xyntillan will be on sale in time for the Holidays; at the moment it is in the proof stage.