Fairy Tail (2014) Episode 59 -

It introduces the Nine Demon Gates of Tartaros, who use "Curses" instead of Magic, making them feel like a unique and overwhelming threat.

It features Wendy’s backstory with "Jellal" and Lucy’s hard-fought victory against Angel. Fairy Tail (2014) Episode 59

Most viewers asking for are referring to the start of the Tartaros Arc (technically Episode 234 overall). It introduces the Nine Demon Gates of Tartaros,

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. who use "Curses" instead of Magic

This episode is widely praised for shifting the show into a significantly darker, higher-stakes tone.