I approve of the first part of your comment:

It's very important to have things going on outside of your friendship. Passions, hobbies, fulfillment. Toxic behavior doesn't affect you like it does when you're very grounded and secure in who you are and what you value. You are able to more easily put into perspective your friendship and what it means to you.

This is not simply true of friendships but of everything. At one point when I was having a lot of trouble at my workplace I was told that everyone needs to have three things, work, family and hobby. Obviously you can mix that up but the essence of it is you need three pillars at any given time, so if one is going to hell you've got other spaces to draw strength from. With that strength you can avoid problems of perspective and avoid making rushed/panic decisions.

The second part of your comment regarding mirror behaviour I don't really agree with - or at least, it's not a good starting point. ideally you want to be able to have a quiet talk to your friend in a private space and talk about their behaviour in an adult, rational way. When you mirror you risk causing them all kinds of hurt that you can't see - they may stop the behaviour but not for the right reasons. If you can pull them aside at the right time and have a quiet discussion you offer a much greater gift - a level of insight into their own behaviour that can enable lasting changes across all their social circles and in many other aspects of their life, with a far lower risk of damaging impact to them. Even better, they may then return the favour one day and you'll get a much stronger relationship out of it.

Sometimes that won't work - maybe they're just a kind of acquaintance, maybe they don't respond well to one-on-ones etc but for the most part a good conversation about a problem should be your goal, it pays off so well.