https://screenrant.com/tv-shows-change-narrative-style-one-episode/

These TV shows boldly transformed their storytelling for one episode to elevate the narrative, creating 10 unforgettable small screen moments.

Musical episode where something of a must in the late 90s early 2000s, and besides "Hush" I would've add also from Buffy the musical episode "Once More with Feeling".

Roseanne oniric episode "Sweet Dreams" from season 2 should also be remembered.
What the heck I'm gonna make my list this is interesting.

Twin Peaks - s03e08 Gotta Light?
Doctor Who - s03e10 Blink
Buffy - s06e07 Once More with Feeling
Buffy - s04e10 Hush
Seinfeld - s09e08 The Betrayal
Angel - s05e14 Smile Time
The X-Files - s03e22 Quagmire
Roseanne - s02e08 Sweet Dreams
Friends - s06e15 The One that Could Have Been
Married with Children - s07e18 Peggy and the Pirates