Tiangang Thirty-Six Techniques was a Daoist technique that involved the fundamentals of the universe and only people who had reached Dixian were qualified to practice this.
According to the rumor, the immortal Zhenren from the ancient time practiced this Daoist technique not to be extremely powerful but for other purposes.
However, this exceptional Daoist technique was long lost. What Shen Lian had was just the surface of the Tiangang Thirty-Six Techniques, which could allow him to shift the flesh and blood of his body temporarily. He could not turn himself into another species or material, which was possible using the complete Tiangang Thirty-Six Techniques.
When Shen Lian's body and the structure of his blood and flesh began to change, all in a sudden the pressure of the sea disappeared and it made him feel free swimming across the sea.