Extra theme: subpar type combinations.
Grass starter is based on Bellinympha, an extinct lacewing with wings that look like cycad leaves. First form is a lacewing larva that covers itself with foliage (real lacewings do this, except with the skeletons of their prey instead of leaves), second stage is a lacewing pupa that has gone full-on bagworm mode, final stage is a graceful but predatory fairy thing with needle wings. Grass/Bug, high speed with relatively average offenses/defenses, gets access to a bunch of support options like Sticky Web, Spikes, Leech Seed and Defog, HA is Disguise.
Fire starter is a grasshopper mouse, a specialist predator of scorpions that is immune to their venom (instead of causing pain, scorpion venom actually acts like a painkiller for them). First stage is more shrew-like than mouse-like and has a poisonous bite, second stage starts resembling a rodent (maybe a capybara, since there's an unspoken rule that middle stage starters should look goofy) and gets a barbed tail, final form is half rat and half scorpion. Fire/Poison, fast physical attacker with a bunch of extra coverage and some fun toys like Encore, HA is Expert Belt as an ability (extra damage on SE attacks).
Water starter is a mash-up between caecilians, Mesenchytraeus ice worms (which are so well-adapted to the cold that even human body heat will kill them) and Rlim Shaikorth. First stage is a small, pale, cutesy worm that borrows from hagfish and olms, second stage gets some segmentation and an outer "skin" of ice crystals (which it uses to feed its offspring, like how caecilians grow a nutrient-rich "second skin" that is torn off and eaten by their young) that develops into a perpetual blizzard in the final stage. Water/Ice, bulky setup sweeper with access to Coil and Recover, HA is Snow Warning. Should get a brinicle-based unique move and some 'dex mentions about how it flash freezes underwater prey with it.
And shit, this was more of a tl,dr than intended.
