The two blacklists, which are death lists, contribute important aspects of character development in the play in regard to Cassius, Brutus, and Antony.
Before Caesar's assassination, Cassius feels strongly that Antony, especially, should be murdered along with Caesar. Cassius sees Antony as a mortal enemy who will try to destroy them after Caesar's death. Brutus opposes killing Antony, making a very logical (but very wrong) argument that without Caesar, Antony will be powerless and ineffectual. Cassius's objections are ignored; Antony lives to eventually bring down Brutus and Cassius. This is one of several instances in the play in which Cassius yields to Brutus, while Brutus's logic and judgment prove to be disastrously wrong. Also, Cassius's assessment of Antony's likely behavior after the assassination foreshadows events to come.
After the assassination, when Antony and Octavius condemn 100 Roman senators to death by marking their names on a list, Shakespeare develops this scene to show Antony's political nature. He appears no longer emotionally distraught about Caesar's murder; instead, he is shown to be quite ambitious, cold, and calculating as he wields power. This represents a new, previously unrevealed aspect of Antony's character.
There are actually two "blacklists" in the play. Although, one is not so literal as the other. The first list occurs in Act 2, when conspirators are discussing who should be killed along with Caesar. Various conspirators throw out the names of Caesar supporters, and Brutus argues against them (for the most part). The most significant name is Antony's because many of the conspirators believe that he will fight to avenge Caesar's assassination. Brutus, however, wants to be able to maintain the people's respect and not appear to be a butcherer by killing so many people along with Caesar. His opinion, unfortunately for him in the end, is accepted by the conspirators who simply hold back Antony as Caesar is being killed.
The literal blacklist mentioned in the play appears in Act 4 when the members of the triumvirate are discussing their hit list--those whom they will kill to get revenge for Caesar's death. Ironically, Antony is the one heading up the list and marking down names. In addition to wanting Brutus and Cassius dead, he also mentions senators and others who will be killed. In the scene Shakespeare juxtaposes Antony's hunger for power and seemingly blood with Brutus's concern for his and Rome's reputation in Act 2. Brutus, who did not want to appear to be a butcherer ends up being killed by the men of a "butcherer"--Antony.