The Chant

Howdy All - Thought I would type out my experience with this during my play through. What is a Mandacore? These are the "plant/flower" cores you run across in the Gloom sections of the game. Not all Gloom areas have one which can make this tricky. I almost got this doing a regular play through without really focusing on these, but to get this there are a few tips I would offer.

Every Gloom section you enter search around it (sometimes outside a building, a room, an area, etc) for the core. Many of these are connected just to progressing the story.

The big part that helped me complete this was after you defeat a certain boss with the green crystal prism there are two areas that have these enemies you need to kill. One is right next to the lighthouse in the destroyed house just to the right (looking at the lighthouse). The second one is also in a green Gloom area you passed while heading towards the lighthouse. If you take the long way back to the camp instead of fast traveling you should run across it as well.

Worst case before Hannah tells you "this is the last chance before we go." at the end take that time to back track and check Gloom areas.

Hope this helps, let me know if anyone has suggestions on how I can detail this better.