For S2, even the ep8&9 were good. 'The Mind Flayer' & 'The Gate'.

Looks like you like all the finale, like me.

Season 1: vanishing of will Byers

Season 2: The lost sister

Season 3: Mall rats

Season 4: Dear Billy

Here are my favorites

Season 1

The Vanishing of Will Byers

The Upside Down

Season 2

MADMAX

The Mind Flayer

The Gate

Season 3

Suzie, Do You Copy?

The Battle of Starcourt

Season 4

The Hellfire Club

Dear BIlly

The Massacre at Hawkins Lab

Papa

The Piggyback

Season 1: holly, jolly

Season 2: the gate

Season 3: the battle of starcourt

Season 4: papa

S1 Holly, Jolly (episode 3)

S2 The Gate (episode 9)

S3 The Battle of Starcourt (episode 8)

S4 The Massacre at Hawkins Lab (episode 7)