Final answer:
Crouch tricked the Goblet into allowing Harry's name in by using the Confundus Charm (C).
Step-by-step explanation:
Crouch tricked the Goblet into allowing Harry's name in by using the Confundus Charm (C). The Confundus Charm is a spell that causes confusion in the target, altering their perception and judgment. By casting this charm on the Goblet, Crouch was able to manipulate it into believing that Harry was a legitimate contestant.
For example, Crouch could have confused the Goblet by altering its perception of the rules and criteria for selecting champions, convincing it that Harry met the necessary requirements. This would explain why the Goblet accepted Harry's name, even though the age limit had been put in place.
Using the Confundus Charm allowed Crouch to achieve his goal of getting Harry's name into the Goblet without raising suspicion or drawing attention to himself.