Enemies, particularly in RPG bosses with no health bars-(This is primarily why I stopped playing the Mario & Luigi series-For me, this is like having a large number of blank puzzle pieces without a picture or piece count-Both can go on forever and ever with no end in sight; also imagine this scenario: Times are desperate and you can't take much more; should you use your strongest attack with that hard-to-obtain item or risk conserving it by using a weaker attack that may or may not do the job-You don't know)
Bosses that restore their health-(A spin-off of the former, the power your partner's heroic sacrifice or minutes of work suddenly wasted, along with all of your Power Points you had used)
LOADING...-That one's pretty self-explanatory.
Permanently missable events and items-(You know those moments when you're still haunted by not getting that one item because you didn't know about it and now the only way to get it is resetting your game? Yeah, those. I'm also covering when you can't go back and replay levels or see cutscenes that you liked without having to make a separate file)
Insanely hard "just so it can be hard" difficulty/Hard mode-(This one is just developers being mean; I understand the central component of challenge, but some companies just seem to want players to suffer and that's wrong; at least make it so someone with average gaming skills can make it through the story or give those less skilled an "Easy Mode", so they can play too. I also just don't like getting angryor seeing other people get angry)
Hard/Hero Mode-(After you beat a game, sometimes a "Hard Mode" with nothing that unique or with anything to work towards, isn't worth it for some people; Plus, imagine how much better games like the already excellent A Link Between Worlds would be if that effort had been put into the first quest.)
Good Game, Terrible Plot/Plot Points/Rosters...-(On a personal level, this ruined the otherwise great Super Paper Mario, Kirby's Return to Dreamland, Yoshi's Island, and the first three Mario & Luigi games. Did we really have to recover two Cobalt Star parts we lost just because the Bros. got dizzy, or running endlessly on a hamster wheel generator, or the introduction of baby characters that plague spin-offs to this day and the idea that Mario and Luigi couldn't have survived witnout the Yoshis and were carried by a clumsy stork, and a RETCON to boot? You get the idea.)
Incredibly long levels/fights with no checkpoints-(Like bosses that regenerate health and permanently missable events, this one is a matter of the time you invested and all of that ending up to mean nothing.)
"Just for the sake of it" Adult Content-Blood, Needless sexuality, swearing, killing for fun, etc.
Mysoginy, Racism, Religious intolerance, Homophobia, stereotyping, etc.-(As a female, this one's personal and hard-hitting; also, minorities aren't the nicest people in the world; I mean, is it just me, or do Black people in particular seem to be demonized all the time, in media and in real life? I'm looking at YOU, Barret...People of all genders and ethnicities need to be treated respectfully.)