In general, I always try to follow three rules for evolutions, whether they're new evolutions for canon Pokémon or just regular evolutions for Fakemon.
The first one: always change the Pokémon's proportions or general shape. A lot of Pokémon just use head proportions, which is totally fine - your Laplet/Laplad has a much smaller body
compared to its head than Lapras, so it's immediately obvious that it's a baby (my example is also like that) - and pretty much every evolution will have a greater body to head ratio than its previous stage. But if you want to get wilder, you can always expand different amounts in length, width and height, like how Linoone is obviously longer than Zigzagoon but isn't much taller or wider. Or you can change the Pokémon's stance, like going from quadrupedal to bipedal or vice versa, or even gaining limbs like Charizard or losing them like Serperior. But again, changing the body to head ratio is all you
really need! These are just extra ways to emphasize the difference
if you think they look good with the design. (For reference, my personal norm for Pokémon that are basic and can evolve further - not single-stage - is to try to make the full design fit within a box 2.5 times the size of head in each direction, and then just to make every evolution a minimum of one head bigger in any direction.)
The second one: always change the Pokémon's color scheme. It doesn't always have to be drastic! A good example of doing this subtly and without completely redoing the color scheme is the Lillipup line, where Lillipup and Herdier
use all of the same colors, but Herdier just puts more focus on blue and Lillipup on brown; then Stoutland comes along and adds just another shade of each of those colors. Usually, if you want to avoid changing colors too dramatically, the first two stages of a line can get away with just redistributing the same colors, and then the third will add another color if needed; of course, you can also cheat by doing different shades of the same color, like Charmeleon is a different red compared to Charmander but still has almost the same colors in the same places. (Or if you're willing to totally change the colors, like Mienfoo to Mienshao, that's good too! I just felt I should clarify that that doesn't usually have to happen and you can be subtler if you want to be.) As a rule of thumb, the more different the Pokémon is in every other way, the less different its colors should be so that they're more easily connected - Wimpod and Golisopod, for example, are almost the same colors exactly - but that's not a hard law (see the Trapinch line for different designs and different colors and the Charmander line for similar designs and similar colors) and you can break it if you want.
And then the third one: always change the Pokémon's design by replacing, not adding (not subtracting, in the case of babies). For example, Mienshao's whips are a new design that replaces Mienfoo's arms, and Stoutland's mustache has a completely different design from Herdier's even though the idea behind them is the same. It's especially important to replace the head - even Pokémon that barely change at all always have different head designs! And then a point that's not necessary, but can really help: try to think of a
distinct (but still related)
concept for the Pokémon to guide what kinds of replacements you should make - a drastic example is the Litwick line, with each stage designed based on a different light source, or the Chingling line, with Chingling being a bell and Chimecho being a wind chime, but smaller changes like Zigzagoon going from zigzags to straight lines can also work just as well. In many cases, changing the concept basically does the work for proportions and colors for you - the "average Bug" line like Scatterbug tends to go from a long caterpillar to a squat, rounded cocoon to a taller and wider but mostly flat butterfly, and cocoons are usually colored by their silk while butterflies have more vibrant wings, so just considering a different concept immediately presents options for the color and proportion changes. But that's not to say that always has to happen - Nuzleaf and Shiftry are based on the same thing, but Game Freak still did just as good a job of distinguishing their appearances as they did with any other line.
Here's an example of these applied to Lapras!
This is Chorice, a Fakemon from my own project! (It's been planned for a while, but I'm actually glad this came up because its old design is from so long ago that
I didn't even follow these rules; I just redesigned it now to use as an example. XP)
Proportionally, it's pretty much just "smaller body relative to head" like I mentioned - it doesn't actually get any major proportional changes. As mentioned, I
personally often make the basic stage fit within a 2.5 head by 2.5 head box, and this does provide an example of that - but that's not necessary at all!
In terms of color, Chorice is a bit greener and warmer than Lapras, and it loses a color by getting rid of the shell - I'm sure only one of the two was actually necessary (
either losing a color
or changing one should be just fine, and especially since Lapras only has one stage, you could even just rearrange the colors like switching the dark blue spots with the light blue body!).
And then the main driving change of the design was a different concept - Chorice doesn't have a developed shell yet and its body is still soft and young, so instead of being the "Transport Pokémon" or carrying anyone on its back, it guides swimmers and sailors to safety with the sound of its voice, like an inverse/benevolent version of a siren. That's why its horn is hollow (so it can blow sound from it) and what the rippling mark on its back is (it's meant to look like a sound wave, kind of like Noibat's and Noivern's ears). Of course, I also just made some arbitrary changes for the sake of being different - its head looks more like a slug (a bit like Goomy) because I thought it would be cute if it was a little bit derpy-looking - but hopefully you can see how altering the concept a little led to a number of simple changes that made it easy to figure out where to take the design, and hopefully this is an okay example of how to do that by replacing and editing instead of adding and subtracting! (Even the shell, which is totally gone, is replaced by the sound wave pattern so it doesn't just become bare and obvious where something was lost.)
Does that help at all? Obviously Chorice is far from perfect - I don't mean to imply that at all - but hopefully as an example, it might be of some use in showing what I mean by the guidelines I just explained. I think following those often helps lead to evolutions that feel naturally like part of the line without being
too like their relatives!
