Sonic Frontiers' Second Free Content Update Celebrates Sonic's Birthday, Arrives Today - Game Informer

The update is called Sonic's Birthday Bash and will add several features including New Game Plus.

News - November, 2021

Sonic Frontiers Update Gives Sonic Spin Dash Move, New Game+ Mode - IGN

Sonic News Nintendo Life

Sonic News Nintendo Life

Sonic Frontiers: Fast Facts - Sonic's Birthday Bash Content Update

Sonic Frontiers Celebrates Sonic's Birthday With a Free Update

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Sonic Frontiers' Free Update Sonic's Birthday Bash is Out Now - QooApp News

Sonic Frontiers' Second Free Content Update Celebrates Sonic's Birthday, Arrives Today - Game Informer

Sonic Origins, Sonic Wiki Zone