Specifically, for the 4* Sentinel Soulless Demon I just got. I tried pumping Magic, and he hits pretty weak. So I tried switching to green talismans and pumping HP to over 7000 instead (which his basic attack says will improve damage) and he still hits pretty weak. His special ability also seems to not do much, even though I maxed skill shards on it. I see people raving about how good this guy is so maybe I just need to level him more, but I suspect the issue is that I am choosing the wrong talismans.
His basic attack doesn't say magic or physical, just true damage. Anyone know what that is calculated off of? Thanks!