The Gen 5 Legendary names end in ram, rom and rem.
Absol's head is supposed to look like a Yin Yang symbol.
The upper half of Pumpkaboo is meant to resemble a bat.
Tympole has music note-shaped eyebrows because the Japanese word for tadpole and music note is the same. This probably inspired the whole line. Tympole uses vibration to make sound, and its evos do it like Tesla's oscillator, making earthquakes.
Beartic's beard is made of frozen snot from when it was Cubchoo. Look close and you see it originates from its nose.
The name Beartic is also actually pretty clever, as aside from it incorporating bear and beard in one, the word arctic comes from Greek arktos meaning bear. (because ursa minor and ursa major are very prominent in arctic regions.) And polar bears live in arctic regions.
Stantler is based on a deer-scarer.(scares deer away from gardens, like a scarecrow.) This is why its antlers look like eyes and strike fear into those who look into them. It's a reverse deer-scarer, frigghtening those who encounter it. And it also works off the idea of "a deer caught in headlights", again in reverse. It also gets Frisk which is Unobstructed Eyesight in Japanese. It also is never coming to Pokémon Sword and Shield.
Talonflame's name is probably supposed to be not from just flame, but enflame. So the two "on/en" sounds blend together.
Gardevoir's red chest plate is supposed to represent the heart. Not the physical kind, the metaphysical kind that stands for emotion and compassion and such. I feel like an embarrassingly large number of people never picked up on this. It's a Psychic based on emotions and feeling rather than intellect.
Gigantamax Centiskorch has exactly 100 legs.
This might not be true, but I heard someone say that the XX glyphs bordering Stonjourner's brown feet and grey legs are together meant to resemble laced boots. This is because it's a traveler/hiker.