The arrival of Jackal and his explosive power sets a violent precedent for the rest of the season.
Most viewers asking for are referring to the start of the Tartaros Arc (technically Episode 234 overall). Fairy Tail (2014) Episode 59
Alternative: Episode 59 of the Original Series ("Recollections of Jellal") The arrival of Jackal and his explosive power
Fairy Tail (2014) Ep. 59: "Tartaros Chapter, Prologue: The Nine Demon Gates" Fairy Tail (2014) Episode 59
Reviewers from Chibi Reviews noted a noticeable step up in animation quality and music for this specific arc.
There are two ways to interpret "Episode 59" because the 2014 series (Season 2) often restarted its numbering or continued from the original show's count.