I dont know how the devs never fixed those, but some achievements are not working and some are pretty vague.

Kunio-Kun:
I've tested it and isn't working at all. I managed to do it at least 4 times with different conditions.

Octoboss:
I tried many times and its not working too.

Show me the money:
I punched every soda machine (some of them give money), parkimeter, coin machine (Arcade), and 6 coin boxes that makes refference to Mario. If thats not everything....idk.

Bring em on!:
I punched every single enemy in the game. All bosses, from all guides. I unlocked everyone in the Arena mode too. Unless the idea is to literaly never abandon a screen without punching everyone on it.

Paparazzi:
Some say that this one is not working too, I dont know by now

Bummer City and All in the reflexes are pretty vague. i tried to catch the weapon in the air punching it = No success. Also tried to grab it pressing grab = no success. Pressed defense = no sucess

I think Hamlet will be a pain, since a lot of achievements isn't working, how I will know that I actualy saw all the dialogues in the game?
The same goes for Big Boss. Its hard, and I dont know if the achievement will pop. There's only two bosses for me to know about that.

I dont know if theres anyone to fix the game by now, and I realy hope someone can mod it to fix some of that stuff