There are some Pokémon designs that are extremely detailed! Some that come to mind are Giratina, Houndoom, Kommo-o, etc. Of course there are many others! Many Pokémon have a lot of symbolism in their designs, often leading to these intricacies. Which Pokémon do you think have the most detailed design? What do you like about them?
Bisharp has a really cool design It's name is based on the Chess figurebishop, but it has more characteristics of a thief which is a cool difference. Also it's pre evo Pawniard is based on a Chess figure too.
Zeraora, the Pokémon of literal lightning. I think it's quite an intricate design, and even lightning bolts were drawn on the back of his paws, and with him being an electric type, well done (they do the same with Pikachu's tail, but he's not really hard to draw). I just think it's a nice design that pays a lot of attention to detail, especially with the fur and how it's made to look like lightning.
Jynx actually has an intricate design, despite her looking just like a human. Her design aspects actually draw from multiple things, like the stereotypical fat opera singer lady, the yuki-onna, the yama-uba, and ganguro girls. (There’s a full description in the picture below, credit of Bulbapedia). That’s the reason I have more respect for Jynx actually (Well I guess this is more origin than actual design but still)
I've always thought that the Gen 4 legendaries have pretty intricate designs. Back when they were first revealed I actually thought that Dialga and Palkia looked out of place in Pokémon and that they felt more like something out of Yu-Gi-Oh. Which is ironic, given that the Gen 5 legendaries include a Blue-Eyes White Dragon (Reshiram) and a Red-Eyes Black Dragon (Zekrom). In fact, most legendaries have very intricate designs as they are the ones that get the most thought and time put into them (apart from the starters).
Celesteela's design is a perfect blend of space, fantasy, and weird for me Guzzlord's design is a perfect blend of spikes, teeth, and making me cry trying to draw him.
I've always like the amount of detail that went into Yveltal and Xerneas. The vein-like marks on Yveltal, the glowing... crystals?... on Xerneas' horns... it really pulls off the "majestic" part of being a Legendary.
I think that most every legendary Pokémon beyond the first generation qualifies for having an intricate design, and they're just getting more and more detailed. As for non-legendary Pokémon, I think that Pokémon like Talonflame and Noivern have pretty detailed designs without looking too busy. Same with Braviary and Chesnaught.