Baguazhang is the sister art of tai chi, and focuses upon stepping and change.
The training involves:

1. 8 mother palms
2. Circle walking
3. Direction changes
4. 8 palm changes
5. Partner work
6. Freeform self defence

Students are encouraged to move, flow, adapt, respond - spontaneously and calmly.

Baguazhang is particularly effective for applying chin na and shuai jiao.

Chinese grappling/wrestling is called 'shuai jiao'.
It is an umbrella term that encompasses a variety of approaches.

Shuai jiao is not to be confused with Western styles of wrestling.

Yang Cheng Fu and the other famous historical tai chi instructors did not collect forms and styles.
They trained one form and focussed on that.

Form collecting is a modern habit which arises when a student is unwilling to commit the necessary practice to mastering a form.
In short, the student gets bored.

A form is a complete record and repository of the system.
It contains every strategy, skill, movement required to gain a good sense of the art.

Your opponent is also utilising the three dimensions. They have no choice in the matter.

If they swing their right shoulder, rotate their waist, shift their weight into the right foot - in an attempt to hit your jaw - they are employing two dimensions.
They are using the horizontal axis, and moving forwards.

Your response must be applied relative to these dimensions.

If you attempt to oppose the incoming force by using an outward-moving 'block' with your left arm, you are going to meet the full force of their delivery.
This is not tai chi.