Which episode first had pets?

Sorry, I only really played back in EP1-2, so never really paid attention past there.
I'm running episode 2 currently, what's the earliest episode with pets included in it?

Also, if you don't mind doing into the detail, or providing a link, could someone please clarify how much different there is between the episodes? (such as random enchantments on drops starting a certain episode).

Thanks :)

EP1 didn't have Pontus Ferrum map and Nation war system, that's for sure.

I remember having a Peng pet back in the EP2 days, with no pet system it was simply for esthetic looks and pure pleasure of somebody chasing me where ever I did go.

The only big change I last remember was that Ring of Luck +2 stopped dropping or something and became really expensive, all old players who still had a lot of them made quick money.