"Dragon and Tiger Leap" means flying like a dragon and jumping like a tiger. Describe a person's vigorous movements when running and jumping. Metaphorically speaking, do something. The subject of this sentence is "pen character", which is obviously inappropriate to describe "dragon and tiger leap". "Fly" means to fly like a dragon; Like a phoenix dancing. It can be used to describe the power and flexibility of calligraphy strokes. So we can change "his brushwork is dragon and tiger leaping" to "his brushwork is dragon and phoenix dancing".