I recently played a game and I had a fellow imposter subtly trying to frame me for the murders he/she committed. Same thing happened when I actually took out a crewmate. Knowing that I wasn't safe with him around, I called an emergency meeting and exposed him for venturing to security when the rest of the group was in administration well accounted for. He ended up accusing me of being a "6ix9ine" and outed both of us to the remaining crew, this was of course after I was able to favor my reasoning. We still won though.
I never thought a co-imposter should defend you, but I always thought that they would secretly be on your side by not agreeing or disagreeing with your accusations. I just wanted to share this story and see if anyone else had qualities of a good imposter they could share.
Edit: In fact, even the crewmates felt sorry for me after the outing.