I second that. With respect to ankle mobility treatment depends on what's the limiting factor: lack of joint mobility -> mobilisation, or tight calf muscles -> stretching. Not the same thing although many excercises cover both areas to a certain amount. If the endpoint of ankle flexing feels like a hard and sudden stop -> mobilisation, if it is a gradual increase of tension -> stretch. That being said, tight joints lead to tight muscles and vice versa.
Owen Anderson once put out a neat routine
against achilles tendonitis which can be used for ankle mobility too. It works excellent when you got achilles tendonitis but it is an effective ankle mobilisation too. But make no mistake mobilisation of really tight ankes can be a longterm project.
Another thing to consider is squats with the barbell on the knee. I first heard about these from Dreschler's
Deadlift a (lightly loaded) barbell with a double overhand grip and go into a squat, just like while doing a zercher squat but place the barbell on the knees pull yourself into a deep erect squat. Stand so for a couple of seconds and stand up again, wait a couple of seconds and repeat 10--12 times. On the last rep try to really relax the calves and glutes and pull yourself with the shin muscles and hip flexors deeper into the squat, try to get those knees further over the toes.
Note however that especially the upper talocalcalean joint can be a real bitch once it's really stiff. Very poor leverage. A couple degrees more ankle flexibility may take month or even years of work on your own.