Grubbin line - When this line was announced, I was looking forward to using it. Initially, the only disappointment was Charjabug due to me not liking its design. But other disappointments would soon follow. First, Grubbin evolved as late as level 20. Then Vikavolt was revealed to have high Special Attack, low Speed, and below average Attack, even though I was hoping for it to become a physical attacker to set it apart from Galvantula. Now it's more like a poor man Galvantula instead. But the worst thing is that Charjabug only evolves at the Vast Poni Canyon, which is the last island in the game! Luckily, there's still Alola Raichu.
Midnight Lycanroc - This form of Lycanroc is the one that intrigued me the most, yet Game Freak made it worse than the Midday form! It feels like Game Freak secretly favoured the Midday form, and gave it special treatment over the Midnight form.
Lurantis - A Pokemon that's both cute and badass? Works for me! Unfortunately, it's slow and has a shallow movepool. If you ask me, Lurantis looks like it should've been faster.
Salandit line - Don't get me wrong, I think Salazzle is a good Pokemon. The problem is that only female Salandit evolve into it, and male ones don't evolve at all. And which gender is the most common? The male one! This makes me even gladder that I picked Litten as my starter.
Tsareena - The problem with Tsareena is the lack of good physical STAB. Sure, it has Trop Kick, but they should've given it more power, or just distributed it to Pokemon like Hitmonlee, Sceptile, Shiftry, Sawsbuck, and even Lurantis. Additionally, I think Bounsweet feels a bit out of place in this line.
Wimpod line - I really would consider using them if they got different abilities alongside Wimp Out and Emergency Exit. And with different abilities, I mean good ones, and not stuff like Truant, Slow Start, Stall, or Defeatist.
Pyukumuku - What were Game Freak thinking when they made this thing? I don't have issues with its design, it's actually really cute. But its "English" name sounds more Japanese than English, and it gets no attacks outside of Bide, Counter, and Z Moves!
Komala - This thing looked so promising when it was announced. Even though Komala was a pure Normal type, it had a very interesting ability in Comatose, and an evolution could've remedied the pure Normal type problem. However, Game Freak decided to not evolve it for some reason.
Every Pikaclone since Gen 3 - Game Freak, why don't you just evolve your Pikaclones instead of constantly making new ones? Additionally, I think some Pikaclones shouldn't have been made to begin with, like Emolga.