Chapter 2: The only one
The letter reads:
Dear members of the Yoshi residence,
Bowser has kidnapped everyone in the Mushroom Kingdom who isn't his ally. Everyone but you two. Parakarry is probably kidnapped by the time you read this. I overheard him saying he was going to kidnap you two soon. I advise you two to leave the Mushroom Kingdom temporarily and find Mario. You are the only ones who can save us now.
Sincerely, PeachYoshi: I can't take another step. You have to go without me. Take this map. It shows the only way to Isle Delfino since the airport was shut down.
Yoshi gives Baby Yoshi the map.
Baby Yoshi: I can't do it. Not without you.
Yoshi: You are the only one who can save us all now.
Bowser: Let me in!
Yoshi: Quickly! Take the secret tunnel out.
Baby Yoshi: I'll do my best.
Baby Yoshi escapes down the tunnel right before Bowser barges in through the front door.
Bowser: Bwahahahaha!
From inside the tunnel, Baby Yoshi can hear Bowser kidnapping Yoshi.
The only one.
Yoshi's words ring inside Bay Yoshi's head as he goes outside.