It is interesting to see the origins of Bloodstained in Castlevania, and not just being an IGAvania/Metroidvania in style. IGA was the one to introduce an importance of alchemy to the CV series. It's heavily rooted in the origin of not only the Belmont's Vampire Killer, but Dracula himself.
And the act of transmutation was also used with the Innocent Devils of CoD. Interesting to know, in Bloodstained, the effects of alchemy result in colored crystals appearing on the cursed and demons. Look familiar?
Not to mention all the demons of Ars Goetia that have appeared in the CV series since SotN(they never appeared prior to that game). Kinda interesting.