I did some further comparisons of hit-dice and hit points of other current CR 1 creatures, and there are plenty such as the Giant Toad (6d10 + 6), Giant Hyena (6d10 + 12), and Giant Octopous (8d10 + 8) with equivalent or higher HP to the Bombardier Beetle.
That said, those creatures don't often have much in the way of special abilities, so when combined with the Vapor Cloud effect, I think it makes sense to drop the HD on the Beetle to 4d8 + 4. I'm also changing the recharge on the Vapor Cloud to (recharges after a long rest).
Where are these from? I can't find them in any of the 5E preview Bestiaries I have at hand.
Where are these from? I can't find them in any of the 5E preview Bestiaries I have at hand.
Incidentally, all three of the above have HD that are pretty close to previous versions:
The AD&D/3E Giant Octopus is also 8 HD.
The AD&D Giant Hyena (Hyaenodon) is 5 HD, while the closest official 3E equivalent, an SRD Hyena advanced to Large size, is 4 HD.
The 3E Dire Toad from Monster Manual II has 4 HD, although its worth noting that the earlier-published AD&D and 3E Giant Toad have 2 HD.
Giant Hyena, Giant Octopus and Giant Toad are all in the 'Dungeon Master’s Basic Rules Version 0.1'
Giant Toad (6d10 + 6), avg 39 hp, averages to more than double 4d8, avg 18 hp (3E Dire Toad 4 HD)
Giant Hyena (6d10 + 12), avg 45 hp, averages to more than double 5d8, avg 22 hp (AD&D Hyaenodon)
Giant Octopous (8d10 + 8), avg 52 hp, is quite a bit more than 8d8, avg 36 hp (3E Giant Octopus)
So the trend in 5e is to have significantly more HP than prior editions for the same monsters. Remember, prior editions used d8 for HD almost exclusively (a few exceptions would call for d10 in the stat-block, but those were rare). Also, monsters now get their con bonus to HP and while plenty of monsters in 2e had 2 + 2 HD etc, the + portion wasn't as common or as high as it gets in 5e.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.