Sephiroth is fought as a boss several times during the Compilation of Final Fantasy VII. Sephiroth's other forms are Safer Sephiroth and Bizarro Sephiroth.
Final Fantasy VII
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After defeating Safer Sephiroth, Cloud Strife falls into the Lifestream and fights a metaphysical Sephiroth inside his own mind. This boss battle is completely cinematic, as evidenced by how all his stats are 0. Cloud will instantly gain the Limit Break Omnislash even if he has not learnt that skill from Gold Saucer's Battle Square. If Cloud does not use Omnislash, Sephiroth will attack for pitiful damage, to which Cloud will instantly counter and win the battle. It is impossible to lose.
Crisis Core -Final Fantasy VII-
Traitor... You will pay.
Sephiroth using Octaslash
Sephiroth is a boss in Crisis Core. He is fought twice in the Nibelheim Mako Reactor. Virtual versions can later be challenged again in two Missions, as well as Hojo's final experiment of which is labled "Experiment No. 124".
First Battle
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In the first battle, Sephiroth can summon four elemental Crystals, the Fire Materia, the Ice Materia, the Thunder Materia and the Support Materia. He also can use the DMW attack, "Octaslash" and his classic "Heartless Angel" attack which knocks Zack's HP down to 1.
Second Battle
Template:FFVIICC Enemies Now Zack is standing on a long platform and can only attack Sephiroth from the front. After every attack Sephiroth uses, Zack is knocked back further and further. If Zack is pushed off the platform, it is Game Over. Because of this, Sephiroth is generally easier this time and does not Summon the four Crystals.