السَّلاَمُ عَلَيْكُمْ وَرَحْمَةُ اللهِ وَبَرَكَاتُهُ, Is it mandatory to say all the Takbir Intiqaal behind the imam, or can you remain silent?

The Jumhur of the people of Ilm are upon that they are a Sunnah. So whether a person does not say them mistakenly or intentionally, it does not nullify the Salah. However, the Hanabilah are upon that they are mandatory. Either way, you should say them and not neglect them.