In Antigone, what does Teiresias predict will happen to Creon and what mistakes does Teiresias say Creon has made?
As in many other Greek plays, Tiresias speaks with a knowledge beyond normal human ken. He is aware of the will of the gods and can speak accurately of the future.
Just as he warns Oedipus what will happen if he follows up on his plans in Oedipus Rex, Tiresias appears in the last play of Sophocles' Oedipus cycle to tell Creon that his hubris will be his downfall.
"The blind prophet Tiresias tells Creon that he has angered the gods and that Creon is to blame for the people’s prayers going unanswered.[...] Tiresias calls Creon a tyrant and warns him that he will lose his son" (eNotes).
It is stubborn pride and a will for power that keep Creon from yielding to Tiresias' advice. The prophet identifies this as the principal source of Creon's failing, saying "[A]ll men make mistakes, but a good man yields when he knows his course is wrong, and repairs the evil. The only crime is pride."
Although Tiresias points to two practical mistakes that Creon makes ("burying" Antigone before she is dead and refusing to bury her brother), it is Creon's willfulness - his hubris - that stands as his central error. This error of character is within Creon's power to acknowledge.
Unlike Oedipus in the first play of this trilogy, Creon is faced with a choice regarding his future. Oedipus was only given a choice between ignorance and knowledge. He proudly chose knowledge and suffered that pride. Creon's choice is, perhaps, more immediate and simpler than what Oedipus faced. Thus his failure is greater.
His punishment is also greater and might be seen in connection to his political motivations. Creon asserts his rule over that of the gods and his family dies as a result. Oedipus' family was devastated, but his children survived his tragedy (initially).
Tiresias in Sophocles' Antigone is a blind prophet, favored by Apollo who is the god of prophecy. Despite being physically blind to the external sight of things in the present, he has clear vision of the future, and more generally matters of the spirit.
Before the appearance of Tiresias in the play, Creon has decreed that Eteocles' body be buried honorably and that of Polyneices left to rot above ground. This was significant because the proper burial rites enable a spirit to cross over into the realm of Hades and achieve some degree of peace or rest. Burial of relatives with appropriate funeral rites was a crucial and important duty of women and determined the quality of a person's afterlife. Thus Creon's decree is very harsh, although perhaps justified in trying to clean up after a rather prolonged and bloody fratricidal war.
Tiresias claims that Creon has offended the gods by leaving the body unburied and that if he does not yield and bury the body, not only will Creon's son end up dead but also:
It won’t be long before in your own house
the men and women all cry out in sorrow,
and cities rise in hate against you
In Scene 5 of the play, Teiresias tries to warn Creon and save him from destruction. Teiresias tells Creon, "You stand once more on the edge of fate." Teiresias tells Creon that he has made a mistake in not allowing the body of Polyneices to be buried, that this act has separated them from the gods: "The gods are deaf when we pray to them, their fire / Recoils from our offering, their birds of omen / Have no cry of comfort." Teiresias urges Creon to acknowledge his mistake and bury Polyneices: "Do not fight with a corpse." He also tells Creon that his punishment of Antigone is another mistake that angers the gods; he must free her.
When Creon rejects Teiresias' advice and accuses him of being corrupt, the prophet shows Creon his future: " . . . you shall pay back / Corpse for corpse, flesh of your own flesh." Teiresias says that the Furies and the "dark gods of hell" will punish him. His house will be filled with weeping, war will ensue, and curses will be heaped upon Creon by many. Creon takes Teiresias' words to heart, saying "I will not fight with destiny."