It's a general, I'm not able to test this myself. Can someone who has the ability to, test it?
I don't know why you're talking about using two completely separate items that's not really relevant to what I'm talking about. I'm talking about using two similar crisis action buffs which can be used together. I just don't know how they would interact. Like I said reaper challenge gives a Critical Triple Action gem while spirits legacy has gem slots to theoretically slot in said gem to test this. Then I said hypothetically if it does work to add in ancient deity's critical double action special ability to see how that interacts and if the crisis action combo can be pushed further. And for the purposes of semantics speech, critical and crisis mean the same thing being 20% HP or lower.
And can you not just set your HP to one? That is very much a thing you can do with the suicide training item and unequipping it. Or use edging mid battle. Unless you have something auto healing at the start of battle which at that point you would just unequip it because that isn't relevant to the test.