"Cuuute! Why is it called a 'blink' dog?"
"You know, err... in the Magic terms, this one phases like hell."
- educating my sister...
A blink dog is a creature from Dungeons & Dragons, later also appeared in AD&D and also in the newest incarnation of the game, Dungeons & Dragons 3rd edition. I have no knowledge of its appearance in AD&D, but I suppose the thing has not changed that much over time.
Blink dogs are similar to wild dogs, looking like normal dogs, with a brown fur and a little bit sturdier build. They travel in packs, eat elk and other game, and are in many ways similar to wolves.
However, they are very intelligent (but can only bark and whimper, which may limit interspecies communication - of course, this bark language in itself is very expressive). They also have a limited instinctual teleportation ability, "blinking", where they get their name. They are able to blink near their enemy, attack, and then blink farther away, and when hunting, blink around to confuse and distract the prey. (In 3rd ed, these features are equivalent to Blink and Dimension Door spells.) Blink dogs and displacer beasts dislike each other (which is logical because displacer beasts resemble cats).
Personally, I think these things are an interesting addition to the D&D fauna, but require quite a lot of care to make them feasible - due to their intelligent benevolence, they make bad "monsters", and are not easy to communicate with, making them difficult NPCs. However, with some creativity, they can be handled. (Thanks for smartalix and m_turner for some suggestions, too =)
Aaron Allison. Dungeons & Dragons Rules Cyclopedia, 1991. TSR Inc., 1991. ISBN 1-56076-075-0.
Monte Cook, Jonathan Tweet and Skip Williams. Monster Manual, Core Rulebook III, Dungeons & Dragons 3rd Edition, 10/2000. Wizards of the Coast, 10/2000. ISBN 0-7869-1552-8.