Personally, I wouldn't write them up as normal races and wouldn't allow them as PCs. There are only two groups that would bother to consider acquiring them. Cerberus has declared that they weren't controllable, and had no intention of getting any, leaving the Salcians (who had one in captivity).
But Yahg aren't that hard to make:
Yahg
BD 0-6-6-4-3 15
PPD (All) 0
MPD 0-2-1-1-1 -25
Lifespan 81-100 0
RR(Fear) +50 20
Soul Dep 6rnd -7
Rec Type 4 -5
Rec Mult x1.5 -10
Start Lang 1 -5
Req Sleep 8h -5
2 dy w/o sleep 5
sub total -17
St, Co, SD, Me, In, Re, Qu: +2 (35)
Ag, Pr: +4 (20)
Note: St gets a +4 & Qu gets a -4 from Giantism (in addition to above)
sub total: 55
8 Assassin Training
7 Gymnastic Training
6 Natural Physique
12 Outdoorsman
10 MA Training
15 Giantism (+4 St, -4 Qu, reduced crits)
45 Natural Weapons (x3: Teeth, Claws, Horns)
7 Peripheral Vision
30 Tough Skin (Insect: AT11, -40 app)
-10 Bad Temper
-10 Blood Lust
sub total: 120
Assuming
55 Adolescent skill ranks (5)
5 Everyman (5)
5 Restricted (-10)
sub total: 0
-17 +55 +120 +0 = 158
by the chart in the FRP GM Law the race still gets 35 talent points or 5 background options.
The temptation is to make them uber when what you want is the average. You have to leave room for the exceptional individuals who will take control of the groups.
They should be considered a TL 15 race, which could get more negatives, but I'd assume that a player would buy that off. Additionally, if they don't intend to play the aggressive, predatory nature of these creatures, I'd make them buy off those flaws too.
