Any sort of super strength without added toughness and motor control. You'd break your own body let alone everything around you pretty fast. Same for juggernaut movement. Or high jump type flight.
I think this is the way they explained it away. But then other extremely strong supes can lift gigantic things as well. I'm actually OK with them not trying to explain it.
I think that's why I love that series. Each quirk has a consequence to it. One-for-all can store and unleash energy, but unless you use that stored power to reinforce the opposite forces, your bones will disintegrate
Forever War delved into the problems with super strength. The power armor took a humongous amount of training to be used finely enough in everyday tasks and not break something or someone. A simple handshake between someone in power armor and someone without could result in crushed bones or a ripped off arm. A great show of skill in using the power armor was the main character sitting down in office and writing a letter with pen and paper while wearing the armor!
Another great example of how dangerous superstrength is when dealing with non-superstrength people was in anime Beastars where one big carnivore accidentally ripped off the arm of his smaller non-carnivore friend. In-lore was said to be a very common thing to the extent that limb reattachment is a common medical procedure.
I had always wanted my superpower to be flight obviously because flight is the shit. I went to my local theme park after the Batman ride opened. I can hear what you thinking Batman doesn't fly. This particular coaster, they put you in laying down on your back, lock you in and then the bat wing flips you over. Every negative G turn, unless you're gripping onto things with your hands, you just rag doll. Even if you could magically work out flight it would just be a constant painful workout trying to keep your limbs from looking stupid while you're doing it.
Being able to turn into metal/sand/water/bats/lettuce or whatever without additional magic would destroy the structure and state of your brain immediately.
I think you guys are overthinking things too much. In a world in which some magical phenomenon can turn you into a lettuce, all of a sudden you draw the line at brain functions?
Maybe it works like caterpillar goop in the cocoon. It’s goop, and not exactly a caterpillar anymore, but experiments have shown that there’s at least some persistence of being, even after the former caterpillar-goop has become a butterfly. E.g. If you train a caterpillar to react to a specific stimuli with a negative response, the resultant butterfly will respond to the same stimuli in the same way that the caterpillar did.