Karanith

Serafen's Wild Mind passive can turn enemies invisible, according to wiki: https://pillarsofeternity2.wiki.fextralife.com/Wild+Mind

It's a bug. Turning character's AI off helps.

I encountered the same issue on my last playthrough with the latest patch, so it's not just you. Although I did not try turning the AI off, so thanks for the tip. Consider posting in the support forum.

I guess they call him "Brutal Ben" for a reason.

I don't think I've seen this information anywhere: how much damage is inflicited by Blood Sacrificie?

Skaen did not get flanderized, he was deliberataly designed this way. Engwithians wanted kith to be submissive, so they created hierarchy among the gods with Woedica as the queen. But I guess they aniticipated that people would still want to rebel, so they gave them the most twisted god of rebellion imaginable. Skaen does not help his followers change the status quo, he only grants violent revenge (including collateral damage) at a cost of great pain and death. Nobody, except the most desperate, would make that deal. Skaen is the closest god slaves and abused have to identify with and he's so repulsive, no same person would worship him. So they just accept their place in the world. That makes Skaen hands down the most interesting god in Eora's pantheon. Unless I'm missing something and he's just an edgy schemer. That however would be extremely disappointing.

Every paladin subclass starts with a special version of one of the basic abilities (e.g. White Flames for Kind Wayfarers) and picks one more during character creation and every chanter starts with a chant and an invocation. So 4 abilities at level one make sense.