My character ended up with a bunch of fake arrows mixed in with their normal ones. I'm trying to come up with a mechanic to see if I end up using a fake one or a real one. I hoping to have a system where the chance of using a fake one decreases when I use one, or increases if I use a real one. 

Does anyone have any cool ideas?

This is the wrong subforum for this, but I would just use a random number generator. Random number between 1 and the total number of arrows, if the number is less than the remaining fake arrows, it was fake.

Sorry, I thought based on the subforum name it was the most appropriate. Which subforum should I have used?

Thank you for your advise.

I agree with DxJxC about the random number generator. A quiver holds 20 arrows, so roll a d20 and if the number rolled is < the total number of fake arrows, you drew a fake. it would only work properly as long as you kept topping off your quiver with real arrows though. Of course, the easiest thing to do would be to ditch all your arrows and replace them with new ones. 🤷‍♂️

Thank you. Unfortunately I'm in a place where we haven't found many arrows, so I can't replace them easily.

So based on the ideas I have decide to roll a D20 for each quiver to see how many fake arrows are in each one. Then before I make an attack I will roll and if its equal or below the number of fakes it's fake. I'll decrease the number fakes for the next roll. 

It slightly goes in my favour each time as it wont account for using up a real arrow.

At the end of each combat I'll swap to the next quiver. Then after the session I'll randomise the number of fakes again as I restock each quiver.

Thank you for the help.