So, you basically can create physical matter with your thoughts?, that is OP
How it can be exploited depends of what kind of matter are the thought bubbles:
If they manifest as a solid, you can create instant shields, walls or hit people with them.
If they manifest as a liquid, you can basically drown people with your mind or swim through them.
If they manifest as a gas, you can conceal yourself in the fog or conceal traps inside.
If they manifest as plasma, electricity or something similar to fire, well, you know how powerfull is that....
Also, you can easily communicate without words.
Crappy power: you can talk to your body parts