A personal favorite of mine! If asked, I would say it is my current favorite pokemon after a lot of thought. Just why exactly? Lets talk about that.
As we already know, Corphish are exotic pokemon that were imported to Hoenn as pets and thrived. Then they evolve into Crawdaunt which the pokedex describes as "extremely hard to raise" and are presumably released, which explains how you can encounter Corphish in the Hoenn.
When Crawdaunt moves into a pond (freshwater) they become desolate and lifeless, and Crawdaunt challenges anything that draws near. Simply darling.
To be fair, its hard NOT to be a harmful invasive species in Hoenn, I mean look at the freshwater competition Crawdaunt has going-
Not really fair sport
There is a small contradiction in Crawdaunts pokedex entry for Gen4, namely that it says an old Crawdaunt has very scarred claws from years of battle, but also claims that Crawdaunt repeatedly molts its shell. This would remove whatever scars build up.
So either old Crawdaunt stop molting, or they fight so often even in their old age to keep fresh scars. I like the latter option.
Now in Gen4, there is no mention as to HOW Crawdaunt makes a pond desolate. It was assumed that Crawdaunt just ate stuff until everything died, but the Gen5 dex states otherwise.
Apparently Crawdaunt doesn't eat a ponds population, or even bully things to death. Instead it picks things up and throws them out of the pond. I'm serious. Just scoops em right out until all the other pokemon get fed up and leave.
Crawdaunt takes a whole pond for its nest and repels anything that draws near it by (guess what) giving em a nice pinch, and throwing them out. This behavior isn't exclusive to males, and Crawdaunt instinctively beat each other senseless when two meet. I guess this makes breeding hard, which explains why Hoenn isn't overrun by sofa-sized lobsters.
Now let's talk physiology, everyone's favorite. At first it might be tricky to determine where exactly Crawdaunts mouth is-
The blue lines throw you off, as do the several jagged ridges that resemble teeth at the top and bottom.
However, removing them shows us what Crawdaunts actual moth looks like unobstructed-
Yup, its only the little hatch on top of the blue markings.
But why have such confusing face markings? That's because Crawdaunt is one tricky and smart fellow.
Here;s how Crawdaunt wants opponents and threats to see his mouth-
How scary! And intimidating!
But that's what Crawdaunt wants being the big bully that he is.
Building off of this intimidation tactic, Crawdaunt goes through a hard-to-notice change when evolving.
Specifically, Corphish has 2 claws and 6 legs, whereas Crawdaunt has 2 claws and 4 legs.
Though Crawdaunt appears to lose legs, they are in fact still present. Observe-
The back two legs merge together to create a wider, stumpier leg. This likely serves the purpose of letting Crawdaunt stand taller to better intimidate things on land. Big mean fellow!! So smart.
I genuinely don't know why Crawdaunt gains a star when it evolves. Maybe because it looks taller that way?? Really not sure.
Competitively Crawdaunt is always a fun choice. It has access to Dragon Dance (for some reason) as well as Adaptability which makes it more of a wallbreaker than an actual sweeper, especially with its sub-par speed stat.
Funnily enough, it was introduced in the same gen as another Dark/Water salt water pokemon Sharpedo, which we'll get into later. Together, they bully both fresh and salt water, evicting nerds left and right.
Design wise Crawdaunt is a great example of a real life animal given a "pokemon charm" and something about it really speaks to me.