Instructions
Bellum, Evil Phantom
Dodge the purple oozes that Bellum throws your way throughout the battle. When one of these oozes misses you and lands on the floor, it grows into a minion which you must then kill.
Attach your grappling hook to the purple ooze pieces on Bellum's body to peel away his armor. When Bellum's green body is revealed, attach your hook to the top part of his body, then pull him toward you. Stab his eye repeatedly until he retreats to the second level. You will repeat this whenever he is on the first level.
Follow Bellum up the staircase. While strafing around this second level, dodging his tentacles as they lash out at you, shoot arrows at the eyes of each of Bellum's five tentacles. When each tentacle has been hit, Bellum will drop back down to the first level. You will repeat this whenever he is on the second level.
Fight Bellum on the first and second levels until he finally retreats to the third level, then follow him there. Shoot each of his tentacles with your bow and arrow. When all five tentacles are hit, he'll fall back down to the first level. Ciela will then become the Spirit of Time and Courage and assist you in the final phase. Follow Bellum down.
Collect the Phantom Sphere that Ciela releases to empower your Phantom Hourglass. Tap the hourglass symbol when it appears, then draw that same hourglass on your touch screen. When you've drawn the symbol correctly, time will freeze. Stab Bellum in the eye repeatedly until time moves again. Repeat until Bellum is defeated.
Bellum
Collect Ciela's Phantom Spheres and draw the hourglass symbol to freeze time -- and Bellum -- in place. Move to his backside, where his eye is vulnerable, and stab him. Ciela will note how this doesn't harm him, then go to check on his eye. She'll be captured by one of Bellum's tentacles.
Strike Bellum with your sword while dodging his own sword strikes. Eventually, the two of you will lock swords. Rapidly rub your stylus back and forth to break his guard, then stab him in the belly to weaken his grip on Ciela.
Grab Ciela's Phantom Sphere, then wait until you see, through Ciela's view on your other screen, that the eye on Bellum's back has opened. Draw the hourglass symbol to freeze time, then run behind Bellum and stab his eye. Repeat this process until Bellum is defeated.