The Dragon #1 (June, 1976): The Bulette (a.k.a. Landshark)
The bulette was created by Tim Kask. Like the owl bear and the rust monster, it was modeled after one of the plastic toy "prehistoric animals" manufactured in Hong Kong.
The name was derived from the creature's appearance - that of a "bullet". It is described to have been cross-bred from armadillo and snapping turtle stock.
The classic illustration by David Sutherland was subsequently used as the frontispiece for the AD&D Monster Manual (1977).
The Dragon #2 (August, 1976): The Remorhaz
The Remorhaz, illustration by Erol Otus.
The remorhaz was created by Rob Kuntz, likely after Remora, a creature from "The Lair of the Ice Worm", by L. Sprague de Camp and Lin Carter, published in "Conan of Cimmeria" (1969).
The illustration by Erol Otus was his first published colour piece, according to an interview in 2009, here. The remorhaz makes an appearance in module G2: The Glacial Rift of the Frost Giant Jarl.
The Dragon #5 (March, 1977): The Anhkheg
The Anhkheg, illustration by Erol Otus.
The anhkheg, a fearsome burrower, was created by Erol Otus, according to an interview in 2009, here. It appears to have been modeled somewhat after a form of giant beetle.
The Dragon #6 (April, 1977): Death Angel
The death angel was created by John Sullivan. Unlike previous "creature features", it was not included in the 1e Monster Manual, probably because the book had already gone to press.
A highly imaginative creature, the death angel shares characteristics with other undead. This is a great OD&D monster to use, as it is fairly obscure.
John Sullivan also illustrated the covers of The Dragon #10 and #17.
The Dragon #7 (June, 1977): The Prowler
The Prowler, illustration by Erol Otus.
A truly horrifying creature, created and illustrated by Erol Otus. It was later used in the AD&D adventure "The Pit of The Oracle" by Stephen Sullivan, in The Dragon #37 (May, 1980).
The prowler is another creature which didn't make it into the 1e Monster Manual, and so is a great option to release on unwitting player characters.
There were no further "Creature Features" published in The Dragon. The 1e Monster Manual was advertised in The Dragon #11 (December, 1977), reviewed in The Dragon #12 (February, 1978), followed by 1-page advertisements in The Dragon #13 (April, 1978) and #14 (May, 1978).