What was the 1st episode of Farscape to feature a Scarran?
This is not including the first episodes with Scorpious.
The first episode I can think of is "Look at the Princess (Part 1)". The crew visit a planet, and it turns out that Crichton is compatible with the princess, and is forced to marry her.
IIRC the Scarrans are involved because they don't want the princess to inherit the throne, but for her brother to instead.
Scorpius is described by Crais as a 'Scarran half-breed' in the Season 1 finale, well before the Scarrans' proper introduction into the series.
Technically, the first episode to feature a Scarran is 'Back and Back And Back to the Future'. This episode features Matala, a Scarran genetically modified to look like an Ilanic, which is a species described as a genetic cousin to the Luxans. If you are asking which episode the actual appearance of the Scarran race is revealed, it is 'Look at the Princess - A Kiss is but a Kiss'