Shadowcat

This is a power that fascinated me when I was younger, but I stopped paying attention to it as I got older.  Intangibility is what it sounds like.  A person can pass through objects like a ghost.  It seems simple and designed entirely for thieves because they can get into any building.  So, I lost interest until this (things really start around 1 minute):

Let’s get to the tips, but I’m probably going to use Mirio as an example for most of them because he’s amazingly well done.

1. This is a terrifying power to have because of its greatest flaw.  If used improperly or control is lost, the character can (and really should) start falling through whatever they’re standing on.  This means falling out of any vehicles while they’re moving, through buildings from the upper floors, and even into the earth.  Authors tend to avoid this issue because it brings up a question of how they didn’t die when it first showed up, but that can be chalked up to a mental defense mechanism that cuts the power off when in danger.  This does NOT always work if a stronger character loses full control.
2. Two things I never considered with intangibility are breathing and senses.  It makes sense that air wouldn’t enter intangible lungs and light can’t enter intangible eyes to create vision.  You can come up with reasons for these to not be a probably such as allowing oxygen directly in from the surrounding area.  Same goes for light since the two are not solid like what the character normally goes through.  Still, downsides like this can help limit the power of a character who is technically unstoppable.
3. Psychic powers should still work.  Intangibility is only of the body, so the mind shouldn’t be protected by this specific power.  There can be some loopholes such as the character moving out of time or dimensions by a hair, but that should also mean that they can’t communicate with others.  If you’re going to have them become immune to psychics then you need a really big tradeoff.
4. As you can see, intangibility at a higher level doesn’t always mean the entire body.  A character can practice to make part of themselves solid while the rest is ghostly.  This allows them to accomplish actions that require intangibility AND interacting with the environment.  For example, slipping a leg through a wall to trip a guard without exposing your whole body.  Reaching through something to type on a computer without entering the room is another.  Get creative since the human body can be split up in many ways.
5. Yes, it’s funny for a character to phase and lose their clothes.  Don’t overdo that joke and try to keep it tasteful.
6. Since intangibility is only the ability to pass through things, a character using it in combat needs to know how to fight.  Mirio is powerful because he knows how to fight even without using his quirk.  He’s developed a style that uses it to his advantage, but the moves are still part of a martial arts school.  For example, a character with intangibility can throw a punch, which passes through the skin to hit the liver directly.  This requires precision, knowledge of anatomy, and training to deliver the blow quickly.  An untrained hero might clumsily pull it off by surprise, but an experienced enemy will be ready once they see the power.  Combat training is where the characters can gain skills to handle hand-to-hand.
7. In a world where intangibility is a known power, there should be defenses against it in terms of weaponry and security.  More than likely, someone with this ability set out to be a thief or broke into a building.  That means, advanced security systems can come with barriers designed to stop intangibility.  Same goes for guns, which may fire energy instead of bullets for these characters.  Keep in mind that these heroes and villains don’t cease to exist, but simply pass through objects.  They are some kind of wavelength or whatever you want to say to show they are still around since they can be seen.  So, it’s not surprising a scientist or organization found a way to counter it and make a fortune in the process.