Let's Go To Gamma World. Meet... The Cal-Then.

Cal-Then  ("Flying Ripper")

No. Enc.:  1d2 (1d4)
Alignment:  Chaotic
Movement:  60' (20')
        —Fly:  120' (40')
Armor Class:  7
Hit Dice:  6
Attacks:  1 (bite)
Damage:  10d6
Save:  L3
Morale:  10
Hoard Class:  None
XP:

The dreaded cal-thens are 8' long insects with enormous dual mandibles capable of rending even the hardest substances, up to and including duralloy (AC 3) armors.  (They may even be able to gnaw through crystal carbon and neovulcanium armors, given time [see p. 128 of the Mutant Future Core Rules]).  They crave the bone marrow of living prey, and relentlessly tear through anything to satisfy their hungers.

Even more horrifying than their insatiable appetites is their intelligence.  Cal-thens are considered to have WIL scores of 18, making them extraordinarily resistant to Mental Attacks.

Mutations:  Reflective Epidermis (Heat, Cold)

Not-The-Designer's Notes:  The Cal-Then first appeared in 1978 in the 1st edition of Gamma World, by James M. Ward and Gary Jaquet, and again in the 2nd edition of Gamma World from 1983, by Ward, Jaquet, and David James Ritchie.  Illustration by Jeff Easley or Keith Parkinson (specific credit unknown) from the 2e set.

Not-The-Designer's Notes Addendum:  I left these straightforward murder-machines pretty much unchanged, but lowered their AC from 9 to 7 because almost all old school Gamma World bugs have awful defenses.