Man, I've only written the title and I already feel like that guy who showed up and just complained about the tiniest things.
Also, disclaimer: this is an opinion, I'm not attacking anyone who plays casually, I also understand that not all casuals use all of these things
Huge stages. I can never seem to find to myself on these massive stages (i. e. Great Cave Offensive, Temple, and New Pork City)
Stage hazards. they get in the way of the actual, skill-based gameplay (specifically New Pork City, that one bastard who kills you in one hit just exists to irritate me personally. don't look that up)
Stupid amounts of players. Yeah, I get that smash is a party game but 8 fucking players. why not just do multiple sets, half of these stages aren't even designed for or big enough for eight players.
Time mode. I haven't seen anything that encourages kill-sniping this much since *insert game that clearly encourages kill-sniping*
Stamina mode. who asked for this?
Random stages. remember when there was some form of strategy in this game? Yeah, well it's gone.
Items. fuck these. you can just ignore the other player(s) and just grab items and you'll still win. they encourage not playing the game or using a suiting character if you use items, play against 4 or more CPs, and play sonic. see if you need to engage with your opponents once.
Also, this didn't really fit in any of the other sections but if you have enough players than it just becomes a battle of pressing the most buttons the quickest