Sacred 3

Unmissable, story related.

This is the final boss. He has 2 phases. The 1st is easy. Just attack him while avoiding his attacks. Once he's preparing to use a skill, you can interrupt him. This leaves him stunned, i.e. vulnerable. During the 2nd form Zane will summon up two clones and an energy beam will shoot between the three. Stun the clone where the beam stops. If you stun the wrong Zane he'll release a powerful spell that might instantly kill you. Otherwise the 2nd form is similar to the 1st, stun him to make him vulnerable. Upon defeating Zane and completing the mission you'll get the trophy.