Mork & Mindy to You Wish

Mork's character originated from Happy Days

Perfect Strangers' featured a game show segment in which the toilet was provided courtesy of Cunningham Hardware in Milwalkee, WI, owned by Howard Cunningham of Happy Days.

Family Matters was a spin-off of the character of Hariette and Carl Winslow from Perfect Strangers

The family from Step by Step was in the middle of a barbeque outside when Urkel from Family Matters came (literally) crashing in on the jetpack he had built on the last episode of Family Matters.

Boy Meets World and Step by Step both had episodes at Disney World and whiel in Disney World Eric from Boy Meets World met Dana from Step by Step.

On the last crossover theme night listed Sabrina and Salem the cat from Sabrina the Teenage Witch visit Boy Meets World, You Wish, and Teen Angel. At every stop Salem changes the decade the show is set in leave Sabrina to scramble to change the show back to normal.

Crossed over during a crossover night