For which type of attack is multifactor authentication an effective deterrent?

Ping of death is a denial-of-service attack targeting network protocol stacks, not user authentication mechanisms.

Phishing attacks attempt to trick users into revealing their credentials; MFA renders these stolen credentials less useful by requiring a second verification factor, significantly increasing security against unauthorized access even if passwords are compromised.

Teardrop is a denial-of-service attack involving malformed IP fragments, which is unrelated to user credential security.

SYN flood is a denial-of-service attack that overwhelms a server's connection handling, not an attack on user authentication.