A Taste of Power: In The Dawn of Ys, Adol starts with the best equipment from the (chronologically) previous game. With it he can one-hit kill everything and nothing can really hurt him. Naturally, he loses it very quickly and doesn't get it back until much later. In Lacrimosa of Dana, Adol still has his Isis Blade from the previous game, but only uses it during the first boss battle, whereupon it gets lost at sea.
Cannon Fodder: Romun Empire soldiers in Ys IV: The Dawn of Ys are given the weakest equipment in the game.
Canon Discontinuity: This game was dropped from the official timeline as it strayed from Falcom's vision.
Infinity +1 Sword: Leo's Sword is strongest weapons in the game, it's entirely optional and requires a bit of lateral thinking to acquire, but attempting to use it against the final boss will result in you seeing the Game Over screen.
New Game+: The Dawn of Ys gives you the option of starting a new game Silver and Gold Rings'' after beating the game. These let you earn double EXP and Gold respectively.
Police Brutality: Adol becomes victim to this in Ys IV: The Dawn of Ys at the hands of the Romun Empire because he spotted some of its soldiers arresting Karna despite the fact that he did not intervene in the arrest (probably not knowing whether she was being fairly arrested or not), and the soldiers decided to arrest him just for spotting Karna's arrest. He quickly becomes a Determinator who wants to wipe out this empire's invasions of Celceta and Esteria.
Power Glows: Your Cleria equipment gets enhanced into the Eldoran equipment, causing it to glow gold.