I’ll go first.
Winner:
Breaking Bad, season 3 episode 10, “Fly”
Honorable mention:
Community, season 3 episode 10, “Cooperative Calligraphy”
PS: I’m having a hard time categorizing these as real bottle episodes since they don’t feel cheap or “fillery” at all, but they are at least spatially and plot wise confined.
Best friends forever from South Park.
At the end, there is a battle happening off screen that is supposedly more epic than the battles of lord of the rings.
When they pan to it, it’s like 3 soldiers with a few pools of blood.