What do you make of the weight of various Pokemon. For example, why does something like Beautifly weigh as much as a young child, while giants such as Primal Groudon weigh only about a ton. (Primal Groudon seems especially weird in that its almost fifty percent larger than its normal form, but only weighs about one hundred pounds more. Primal Kyogre is even more bizarre.). This seems to be a trend among Pokemon, with small species being super dense, while big ones are ultra light, like Wailord.
This has always bothered me, but upon looking into it, I think many of them actually hold up quite well. In some cases part of the difficulty is that it’s not always clear what a Pokémon’s listed “height” actually means – like, if Beautifly’s body is one metre long from head to toe (does… does Beautifly have toes…? Bah; whatever) then I could easily see her weighing 28kg; if 1m is, say, from the tips of her antennae to the ‘tails’ of her wings, or maybe even a 1m wingspan, then it becomes a lot harder to swallow. In general I’m mostly fine with the weights of small Pokémon.
As for the big ones… well, the thing is, even the largest Pokémon are not usually all that big. If we take, say, Snorlax, whom I’ve compared to a giant panda in the past in ecological terms… well, Snorlax is maybe 35% longer than an average giant panda (1.5m and a little over 100kg, compared to Snorlax’s 2.1m and 460 kg), and if you just scaled up an animal by 35% you’d expect its weight to increase by a factor of 1.35 cubed, or about 2.45 (I will remind you here that I AM NOT A BIOLOGIST), which gives us a rough guess of 250kg or so for a Snorlax-sized giant panda; Snorlax actually weighs a lot more, but hey, it’s Snorlax, so that’s not altogether surprising. You might make a similar comparison between Gyarados and a large giant oarfish specimen – the biggest ones on record approach 11m and 270kg; Gyarados is a similar weight but significantly shorter (6.5m), which makes sense considering that he’s so much more powerfully built. Wailord, I will grant you, is bizarre; he’s almost as large as an adult sperm whale, but weighs less than 10% as much. Wailord is something of an outlier though (being more than 50% longer than Steelix, the next-largest non-legendary Pokémon), and I think that may even be intentional, almost a joke – presumably they called him “the Float Whale Pokémon” for a reason.
I don’t think I’d ever necessarily expect legendary Pokémon to make any damn sense at all, especially not mega-evolved ones and definitely not Primal Kyogre, whose body appears to be composed partly of energy. When do we imagine the authors of the Pokédex had the opportunity to weigh these Pokémon, anyway?