Alabasta Arc
When Ace first meets Luffy’s crew, he tosses them a piece of paper and leaves. However, in the anime, his time with the Straw Hats was extended and he journeys with them for a while. During the journey though, Ace’s bead necklace kept appearing and disappearing in-between scene changes, most likely due to mistakes from the animators.
Mera Mera no Mi
In the manga, it is unknown if Ace can light things on fire from a distance without spouting flames that make direct contact. However, in the anime, he is shown lighting a cigarette for Sanji simply by pointing his finger.
Ambition
During his meeting with Shanks in the anime, Ace stated that he would become the Pirate King. At no point in the manga did Ace show this ambition, but rather he aims to make Whitebeard the Pirate King. Also in the anime, Ace stated that he wanted to show the world his power by taking Whitebeard’s head. Ace’s reason for going after Whitebeard’s head was never explained in the manga.
Marineford Arc
In the anime, the Ace’s and Luffy’s fight against the Marines (after Luffy unlocked his handcuffs) was expanded and Ace showed more of his attacks.
In the anime, when Ace was struck through by Akainu, his beaded necklace broke apart and fell all over the ground, and one bead ended up rolling to Whitebeard’s foot, who picked it up tearfully; in the manga, the necklace remained intact. Ace also was covered in less blood than in the manga, and the smoke coming from his wound was absent. Other oddities include most of the artwork being largely uninspired by the manga.
Ace’s chin covered blood in the manga.
Ace’s chin showing only thin streaks of blood in the anime version.
Ace’s death in the manga, which shows more blood and his wound still smoldering.
Ace’s death in the anime that hardly shows any blood at all.
The following episode, however, increases the amount of blood.
In the anime, Ace’s beaded necklace was destroyed moments before his death.
In the manga and the special episode3D2Y, his necklace is still intact.