Probopass because you know that Gamefreak must've been smoking some kind of mushroom while designing it. Oh you meant literal mushroom Pokemon. Okay well in that case Paras because it was cute in its debut episode. :3
I love Shroomish! I didn't liked Brellom but I got along with it after a new playthrough in Sapphire and I made sure it was in my AS team, despite my starter being a Chespin.
My second favorite is Parasect, because it's just a zombie controlled by the Grass-type mushroom (now that I write it, it would be awesome to have the mushroom come out or fusing with and being the final evolution stage of Paras!!). Paras is just cute.
I like Amoongus and Fongus but I never took the time to train them since I prefer other same type Pkmn, namely Victreebel, Venusaur, Roserade and Vileplume. Perhaps I'll give it a try in a new playthrough of White.
When it comes to Foongus and Amoongus, I like their design and their entries (the first is cute, the second is creepy) but I'm not that into Fairy types and the fact that it debuted in Alola, made me not paying attention to it. I expect to train some in future games.
Definitely Team Morelull, especially with its very mystical and cute depiction in DP, I love its design. Sort of sylvan in a fairy-like way, while not coming off of as the traditional "parasitic" or "fungal" Pokémon. Really likes its lavendar/purple-ish tones too.
Morelull is so cute and pretty. I'm a huge fan of real mushrooms (they can look so freaking cool!) and the moment I saw Morelull I was in love with its design. (If you take away Shiinotic's mouth I'd feel similar to it...)
Man now I want a dark type mushroom pokemon based off those ink cap mushrooms.
I like creepy Pokemon; so my favorite mushroom Pokemon are the cordyceps-based Parasect line and Shiinotic line. I particularly like Shiinotic and how it's like a freaky-ass Toad/Petey Piranha hybrid, and it happens to be a Fairy type, too.
shiinotic is my favorite mushroom pokemon (I appreciate morelull too). It's delightfully eerie, with its alien-like appearance and tendency to cause people to get lost in the woods with its bioluminescence. Parasect is my second favorite, it's a creepy zombie bug that's had its body hijacked by a fungus. The fact that my two favorite mushrooms in the pokeverse have feuds over territory is neat worldbuilding. I also have a bit of a soft spot for foongus, simply because I find it cute.
My top favorite mushroom Pokémon are definitely Morelull and Shiinotic; those fulgent fairy fungi are just so frigging fabulous! Paras and Parasect make a close second, considering that I love both mushrooms and bugs, and the mushroom’s takeover of Parasect’s body is interesting of course. I’d rank Shroomish and Breloom third, since Shroomish is a cute little grump and I’ve wanted to experiment with Breloom in battle for a long while now. Foongus and Amoonguss are pretty interesting too, even if they don’t stand out to me as much as the other three mushroom Pokémon families.
I wonder what mushroom Pokémon Gen 9 will bring us years later?