My cat has been stretching at one of his ears for a couple weeks now. Tonight its has a bad smell, brownish, black liquid in his ear. I noticed in his ear canal there is a red bubble that wasn't there last week. I can't take any pictures because he never stays still long enough.

It sounds like your cat may be dealing with an ear infection. Ear infections can be caused by bacterial, parasitic or fungal infection, or a combination of these, and can be associated with dietary or environmental allergies or sensitivities, immune system disorders, or a combination of the above. Your cat needs to see a vet. Your vet can look at a sample from an ear swab under the microscope and treat appropriately based on what is found. Your vet will also need to examine the ear with a scope to see if the ear drum is intact, as some medications cannot be used safely if the eardrum is ruptured. Ear infections can be very painful, and can sometimes progress to include the middle or inner ear, where they can cause neurologic signs or permanent hearing loss. Please book an appointment to have your cat seen by a vet as soon as possible. Good luck!

This sounds like an ear infection that may have ear mites to go with it. If you have any pet ear cleaner you can try to rinse the debris and black material out as this may help relieve some pressure. The red bubble may be blood or swelling of the ear canal from the infection and constant shaking and scratching. You will have to see your vet tomorrow to have prescription medicine in order to clear the infection and see if there are any mites that need to be treated also.