Okay, so, in the Pokemon games, sexual dimorphism has been a thing since Generation 1 introduced us to Nidoran♂ and Nidoran♀, however it got a HUGE shot in the arm in Generation 4, which made it so various Pokemon species, both new and already-existing, had sexual dimorphism traits- some of them hard to spot (see: Torchic), but some of them glaringly obvious. And it's far from the last generation to have them, either. They've been around for quite a while.
Thanks to Gen 4, we know that female Pikachu have heart-shaped cleft tails, that female Wobuffet have "lipstick", and that female Shinx have blue hind feet instead of black. And heck, later on we got introduced to Pokemon like Unfezant, Frillish, and Meowstic, who look remarkably different depending on gender.
- Male Unfezant have green "pants" and a mask, females have brown "pants" and no mask.
- Male Frillish and Jellicent are blue, and the Jellicent have a Pringles-Guy-style mustache. Females are pink, and the Jellicent have a "ruffled collar" and exposed mouth.
- Male Meowstic are blue with white accents, and have blue and green, open eyes, while females are white with blue accents, and have yellow and red, half-closed eyes.
For all of these Pokemon, we have sexual dimorphism. We have SECONDARY sexual characteristics to look for, evidence that should be far stronger than body shape and clothing. ...However, from what I've seen, TWYS apparently doesn't let us use that knowledge??
Hell, just look at this picture. It's of a Meowstic, and we can instantly see from the blue fur and the eyes that it's supposed to be a male Meowstic. You can't even have the "It might've been drawn before gender differences were a thing" as an excuse- Meowstic was introduced well after sexual dimorphism as a mechanic were established, and was designed around it, with males and females working differently in combat. (They learn different moves, with males having more status moves and females having more attack moves- and they have different hidden abilities, with males getting Prankster and females getting Competitive.)
However, that very post got locked tags from an admin, locking it to "Ambiguous", "Ambiguous/Male", and "-Male/Male".
Or what about this one? It's of a Pikachu, and a very specific one at that- Cosplay Pikachu, in her rather popular "Pikachu Libre" outfit. Now, I don't want to get into Cosplay Pikachu as a character being enough knowledge to tag- because this site has proven that it's not. Instead, I want to focus on her tail.
In that pic, we see that she has the heart-shaped tail that denotes that she's female. Hell, it's even tagged- a brief glance at the tags reveals "Cleft_Tail", a tag almost exclusive to female Pikachu (there are a few instances of the tag given to non-Pikachu characters, but they're few and far between, as a simple search of "cleft_tail -pikachu" can attest to.) But for some reason, it isn't enough to denote that the Pikachu in the picture is female- the post itself is currently tagged with ambiguous_gender instead.
TWYS needs to be consistent on this. If body shape, eyelashes, and clothing choice is all that needs to be visible for one type of mouse to be "female", then a heart-shaped tail should be all that needs to be visible for another type of mouse to be "female".
Updated by SnowWolf