Cheers for Fears, Steampunx

When Candace is stumped about what to get Jeremy for his birthday, she reluctantly asks Phineas and Ferb for their help in creating the ultimate gift. Meanwhile, Doofenshmirtz plans to make fears a reality with his Worst-Fear-Inator, but his plans backfire when he finds himself battling his own fears instead.
When Phineas and Ferb discover a commemorative coin from the 1903 Danville World’s Fair, Lawrence recounts the events of the festival to them, in which steam-driven devices were introduced and a set of kids, who were very much like them, were preparing for the highly anticipated event.