Just an exercise I wanted to do, of final evolutions:
Pokemon with Spikes (level up or Egg Move)
Of these, which would you say don't look like Spikers? I'd say Forretress (no sharp protrusions, just the cannons), Deoxys-D (way too smooth), and Froslass. Glalie and Skarmory are on the edge of sense, with one or two spiky protrusions, but Skarmory looks more offensive with those wings. Still, there is a theme with the majority of Spikers: rounded bodies, mostly armored, and spiky protrusions.
Let's try Toxic Spikes next:
Again, what doesn't seem to fit? Venomoth, in my opinion, Forretress as well. To a lesser extent, Tentacruel and Roserade, but they work off of the assumption of cnidocytes and rose thorns, respectively. Still, another theme: Pokemon with sharp protrusions, who happen to be associated with stinging or puncture injuries, who also are poisonous.
Gravity is where things get interesting...
Four of these Pokemon are "cute", three of them are squishy and balloonish. One is a ghost, and one happens to be a god. Still, the theme for Gravity seems to be mostly cute, squishy, and pliable.
Tailwind brings up one interesting counterexample within its list of users:
Suicune, the only non-avian on this list, is here only because it is "said to be the embodiment of the Northern Wind". All others are Flying types. Thus, if we want Tailwind, well, we need something that makes sense for generating gale-like forces.
Trick Room would spam the page with users, thanks to it being a TM. The general theme is Psychic Pokemon, yet the only Pokemon to learn it by level up is the Glitch Pokemon, Porygon-Z. Non-Psychic TM final evolutions besides it include Gengar, Kecleon, Spinda, Dusknoir, Palkia, Dialga, and Arceus, the final three obvious in their relation to space-time.
Our Wishing Pokemon theme is either cute-wish making, like Clefable, Togepi, etc, or more psychic-prophetic, like Xatu, Gardevoir, etc. I wouldn't say Illumse fits into the first category, but I could be wrong.
Our Rapid Spinners have a way of retracting their limbs into their shell / against their body, or are circular enough that spinning with their limbs out doesn't cause problems, or something. Blastoise, Forretress, Donphan, Sandslash, Cloyster, and Kabuto fit into the first, Starmie, Hitmontop, and Tentacruel into the other. Hitmonlee and Delibirt seem to be outcasts here.
Encore users would have hands, or are very vocal. There are some obvious counterexamples, but my hands hurt too much from typing this up in one go.
TL;DR: Spike protusions implies Spikes, poisonous Pokemon with said protrusions implies Toxic Spikes, cute Pokemon use Gravity well. Hands or vocal for Encore, small body, rounded body, or retractable limbs for Rapid Spin, cute or "prophetic" for Wish, strong winds or flying for Tailwind, space-time distortion or psionic powers for Trick Room.