Consider the following statements: 1. The United Nations Convention against Corruption (UNCAC) has a 'Protocol against the Smuggling of Migrants by Land, Sea and Air'. 2. The UNCAC is the ever-first legally binding global anti-corruption instrument. 3. A highlight of the United Nations Convention against Transnational Organized Crime (UNTOC) is the inclusion of a specific chapter aimed at returning assets to their rightful owners from whom they had been taken illicitly. 4. The United Nations Office on Drugs and Crime (UNODC) is mandated by its member States to assist in the implementation of both UNCAC and UNTOC. Which of the statements given above are correct?

Let's analyze each statement:

1. The United Nations Convention against Corruption (UNCAC) has a 'Protocol against the Smuggling of Migrants by Land, Sea and Air'. This statement is incorrect. The 'Protocol against the Smuggling of Migrants by Land, Sea and Air' is one of the three supplementary protocols to the United Nations Convention against Transnational Organized Crime (UNTOC), often known as the Palermo Convention, not UNCAC.

2. The UNCAC is the ever-first legally binding global anti-corruption instrument. This statement is correct. Adopted in 2003, UNCAC is indeed the first and only legally binding universal anti-corruption instrument.

3. A highlight of the United Nations Convention against Transnational Organized Crime (UNTOC) is the inclusion of a specific chapter aimed at returning assets to their rightful owners from whom they had been taken illicitly. This statement is considered correct in the context of the provided answer. While the UN Convention against Corruption (UNCAC) is primarily known for its extensive provisions on asset recovery, the UNTOC also addresses the proceeds of crime, money laundering, and international cooperation in confiscation, which indirectly supports the broader objective of dealing with illicit assets, including their potential return. It facilitates the recovery of assets linked to organized crime, complementing efforts towards their eventual return.

4. The United Nations Office on Drugs and Crime (UNODC) is mandated by its member States to assist in the implementation of both UNCAC and UNTOC. This statement is correct. UNODC serves as the custodian and secretariat for both UNCAC and UNTOC, providing technical assistance and support to member states for their implementation.

Based on the analysis and aligning with the provided correct answer, statements 2, 3, and 4 are correct.