"An Old Nemesis Returns" (宿敵との再会, Shukuteki to no Saikai) is episode 265 of the Naruto: Shippūden anime.
Receiving intel from headquarters that enemy troops were travelling underfoot, Mifune redeploys his division to support the others. Elsewhere, Sai, Zaji and Omoi of the Surprise Attack Division launch an aerial attack using explosive tags on a group of reincarnated shinobi that they located, but the enemy recover from the damage quickly. Responding to the threat after protectingZabuza, Haku launches an aerial attack on the three shinobi using one of his mirrors. Seemingly in peril, the three shinobi are saved by the Third Division who had seen Zaji's signal flare. Confronting Zabuza once again, Kakashi Hatake speaks to him and Haku about Naruto and his growth. This reunion, however, is cut short in its niceties as Kabuto Yakushi — who had just drained Anko Mitarashi of the remaining dregs of Orochimaru's chakra — eradicates their personalities as he prepares to have them attack. As the battle gets under-way, Zabuza covers the battlefield in a thick mist under the cover of which the reincarnated shinobi attack. Cautioning his troops before they attack, Kakashi tells them to get into the Manji Formation in order to protect each others' backs. As the battle wages on, Pakura uses her Scorch Releasekekkei genkai to essentially mummify the shinobi she attacks while Gari, who had engaged in battle with Tajiki, uses his Explosion Release to blow him to bits. Seeking reprisal, another Kumo-nin attempts to attack Gari and is almost killed by Haku if not for Might Guy and Rock Leeintercepting the young man's attack and repelling him. Intending to keep the upper hand in the battle, Kabuto uses Gari and Pakura to summon the previous generation of the Seven Ninja Swordsmen of the Mist much to the shock of the onlooking Third Division.
When Kakashi is remembering when he fought Zabuza in the beginning of the episode, Zabuza's sclerae are shown black as if he was resurrected back then.
There are some inconsistencies between the flashbacks and what was shown originally:
Originally, Zabuza requested Kakashi to place him by Haku's side. In this episode, Zabuza approached Haku instead as he was dying.
The scene when Gato kicks Haku's face was not shown originally. In this episode's flashback, the kicking scene is shown.