Margit, the Fell Omen is the first story boss you’ll encounter on your way to Stormveil Castle. If you’re having trouble with him, there are a couple of things you can do to make things easier.

Fell Omen - There are two here, one for if you fail, and one if you succeed. If you die while fighting the Fell Omen, on top of losing a level, ...

The Fell Omen's sudden invasions have hopes high for other enemies to suddenly appear and attack the players. The Pursuer from Dark Souls 2, for example, would make a great candidate.