Displacer Beast

This vaguely puma-like creature is bluish black, its tentacles are dead black, the horney edges of the tentacles are brownish yellow, and its eyes glow a hellish green.

A pack of these monsters always contains only full-grown beasts. These fierce creatures hate all life, but they particularly hate blink dogs.

In combat the displacer beast lashes out with its two tentacles, inflicting horrible wounds with the rough, horney edges of these appendages.

The molecular vibrations of the displacer beast are such that it always appears to be 3-ft (left, right, ahead, or behind) its actual position. Thus, these monsters always cause opponents to subtract 2 from attack dice rolls and add 2 to their dice rolls for saving throws. 

This greatly feared beast resembles a large leopard with 4-7 snakes sprouting from its shoulders — it is clearly a relative of the displacer beast [...] though how it became such a curious cross-mutation is a matter for speculation.

In melee the creature attacks with two claws for 1-3 hit points of damage each and bites for 1-6 hit points of damage. 

Each snake will also bite for 1-4 hit points of damage, though the snake bites are not poisonous.

It also has a breath weapon — a cone of sleep 30-ft long and with base diameter 10-ft. 

This puts creatures of 4 dice and below to sleep — no saving throw allowed; creatures with more hit dice are permitted a saving throw as against dragon breath.