Something's A Little Fishy by Phineas
The "Too Young" Line
Ferb: Put ice cream on the fish, and WA-LA!
Phineas, Baljeet and Isabella: Ugh! That's gross!
Isabella: Hi, Phineas! Whatcha doing?
Phineas: Ferb, Baljeet and I are making this golden fish EXTRA SPARKLY!
Perry's Entrance to His Lair
Through the floor like in "Fireside Girls Jamboree".
Doofenshmirtz's underground tunnel!
Perry enters his lair through the floor ("Fireside Girls Jamboree")