Very minor, but an antagonistic side character asks Bree (who is underage) if she is providing a "helping hand" to Nick in exchange for being in the tournament
Although there isn't gaslighting per se, memory manipulation is a power that certain characters in this story have. They can replace characters' true memories with false ones.
Whipping and other tortures of slavery are described. The character witnesses someone whose back is severely injured from having been whipped. When a character starts removing a prisoner's memories, this act is described as a form of torture.
There are demons who behave in ways similar to ghosts. There are also scenes where the protagonist and others send their consciousnesses back in time in order to witness ancestors who have died.