This Seeking Tech guide will show you how to beat the last boss in Final Fantasy IV Pixel Remaster.
Before the actual fight starts, you need to use the Crystal item on Zeromus.
After he transforms, Rosa should focus on healing with Curaja while Cecil provides backup with Cura.
When it comes to attacks, Kain should use Jump, Rydia should summon Bahamut and Edge should throw shurikens. If there isn’t any need for any extra healing, Cecil can use his regular attacks.
Make sure you keep your party at, or close to, full health since Zeromus can attack in quick succession.