Righteo! Cheers. So, they were just more frequent and deadly? I'm totally cool with that.
They're just buffed up versions of regular enemies. More HP and more damage. Then there are also black phantom versions of a few NPCs, which are immediately hostile. They're also stronger than the regular versions of those NPCs.
Some BPs are really dangerous. The most dangerous one I've found in Demon's was the BP dual katana skeleton (found on black world tendency in 4-2). I thought the regular one was annoying but the BP version is way worse. He was able to kill me in just a single swipe.
Luckily when I fought him I had the Second Chance miracle (revives you once if you die) on. You can use Second Chance again if you die (so long as you have the MP, and you can use MP restoring items if you don't) but it's still a struggle to find an opening to use items and the miracle before he hits you one more time and kills you. After doing this repeatedly I figured he was becoming too dangerous to fight with melee and I managed to lure him way back and kill him with arrows.
People were bringing up BP Satsuki earlier...dual katana skeleton would eat his lunch if they fought. Satsuki is only really annoying because of his healing, otherwise he's not too bad.