Tavis at The Mule Abides sent me a question that made me realize for the first time how surprisingly much hell hounds differ between editions of D&D. (The question being: "How to use hell hounds in Book of War?")
Hell hounds first appear in the OD&D Greyhawk supplement, where it is written:
The damage caused by their fiery breath corresponds to the number of hit dice they have: hit dice range from a low of 3 to a high of 7 (6-sided dice). [OD&D Sup-I, p. 38]
Notice in regards to this breath attack that (unlike, say, dragons) that there's no range, no time or charge limitation, and no specification as to what "corresponds" exactly means. Now consider the evolution into the B/X line, as seen in the Rules Cyclopedia:
A hellhound will attack one victim, either breathing fire (one chance in three: 1-2 on 1d6) or biting (two chances in three: 3-4 on 1d6) each round. The breath does 1d6 points of damage for each Hit Die of the hound. The victim of the breath may make a saving throw vs. dragon breath to take half damage. [Rules Cyclopedia, p. 184]
So here we have range (namely, one victim), a usage limitation (random 1-in-3, but otherwise usable any number of times), and an explicit damage specification (namely, 1d6 per Hit Die). A powerful ability! Now compare to AD&D:
In addition to a normal attack (simply biting with their great black teeth), hell hounds breathe out a scorching fire at an opponent up to a 1" distance, causing 1 hit point of damage for each hit die they possess, unless the opponent is able to save versus dragon breath, in which case only one-half damage is inflicted, i.e. a 7 hit dice hell hound breathes for 7 or 4 hit points of damage/attack. [AD&D MM, p. 51]
Consider the difference. Again we get an interpretation of range (1" distance), but no restriction on usage (presumably unlimited), and a surprisingly underwhelming damage potential of just 1 point per monster Hit Die. (Notice the text example is for the largest possible type of hell hound.)
I do keenly recall running AD&D hell hounds in a higher-level game, not looking too closely at the statistics before play began, breathing fire on the players and watching them tensely roll saving throws -- and then marking off maybe 2 or 4 points of damage in a rather bemusing, anticlimactic result. Interesting to discover that the B/X branch of D&D did something a lot more significant.
I actually think I like the B/X interpretation more for the game -- breathing fire needs to have some punch to it, one that higher-level PCs would really want to avoid. Compare to dragons, that do points of damage = dragon hit points with their breath (or, equivalent to dice of damage = dragon Hit Dice on average). Hounds doing a similar thing would then resemble mini-dragons in scale and mechanic (hell hounds NA 2-8, HD 3-7; the smallest white dragons NA 1-4, HD 5-7). Maybe apply the same 3-times-per-day limitation if going in that direction (although as usual, use 1-in-3 rounds would usually amount to the same thing in most fights).