biting your cheeks relatively dont do anything AS LONG as you dont bite to hard, but it sounds like it could just be a hyperpigmentation (moles) or a leakage from a tooth filling, if its round like a plum it might be a blood blister like someone else said. always check with a parent or adult first though.

Oh-
Idk what that is

Blood blister are 100% not dangerous or causes anything bad to your mouth unless if you touched it many times it is not harmful since its small you’re lucky, try drinking salt water to make it heal faster it actually heals by its own but salt water makes it heal faster so i recommend drinking or splitting the salt water i heard from lots of people having the same problem like you kept on saying it only takes a week or 10-13 days to go away it is way too normal just stop biting your cheeks, sigma faces wont help you bestay 🤨

Girl i think thats blood blister cause you said you bite your cheeks just to looks like sigma 😨

for gods sake yall help me i swear i love u guys