To get oversplits, good to first warm up doing splits on the floor, then with one foot on a panel mat, higher and higher as you get better at it. To get a better pancake and pike stretch sometimes it can be better and easier to get someone to push you down a little and help you go down further and further - when you got the stretch pretty good, then it's easier to do it by yourself. To increase the flexibility on pancake you can put your feet on a small mat to be a little higher, and then higher and higher as you get better at it.
The ways of coach stretching oversplits can also help with pike stretch and the ligaments stretching - as long as it's not too extreme and you don't pop!