Kastro

Kastro is a prominent fighter in the Heavens Arena and apparent celebrity.

Backround
Two years prior to the start of the series, Kastro was defeated by Hisoka in the Heavens Arena making it his only loss. After this, he trains rigorously to improve his Nen and gains nine wins and then challenges Hisoka for his tenth.

Heavens Arena arc
Kastro is a fighter that lives on the 200th floor of Heavens Arena with the intent of accumulating enough wins to become a Floor Master. He challenges Hisoka to a rematch. Kastro's undoing was in the type of Hatsu ability that he had chosen. Although he was born an Enhancer, Kastro's "Doppelganger" ability completely ignored his strengths and used Conjuration and Manipulation abilities. An Enhancer's maximum ability in these fields is 60% at best, so for Kastro is difficult to use and requires a lot of nen and concentration.

Despite this Kastro combines his two abilities to cover the defects of his double, making a letal combination, but Hisoka take advantage of Kastro's weaknesses, distracts him with his abilities and ultimately kills him.

Combat
Kastro demonstrated to be a very skilled fighter with considerable physical combat skills that excels in hand to hand combat.

Trivia

 * His battle with Hisoka was mostly omitted in Nippon Animation's anime adaptation.