From EsoArcadia's Skies of Arcadia wiki
Grendel (Gigas that lives under the Green Moon.) is a
|Skies of Arcadia Ship Enemy|
- Even though you're not supposed to, it is actually possible to completely deplete Grendel's HP. However, the story progresses as if you did what you were expected to do, which is push Grendel into a chasm.