My cat has been acting kind of...strange?

Ooh, he's getting old and maybe a little ornery! I'd get him to the vet to make sure he's healthy. If you have already, I'd say he's probably bored and playing to keep himself entertained. Keep an eye on the old guy. Lots of times, the older ones are inactive, so you're lucky with him keeping active. If his deafness is new, he's freaking out a little, so maybe you can keep him distracted or at least tire him out with visual toys, like a feather fishing pole or a laser light. Good luck!