Baron Samedi and Hekate Guide
First thing to note: those two characters don’t exactly work together. They both want all the APs to do their thing, so you’ll need to either just take one or, if taking both, be content with one of them being a support.
Samedi: Depression is not a weak DoT. In addition to dealing damage it also lowers the maximum SP of the victim and it can be boosted with relics and Samedi skills. The one thing he lacks is the ability to effectively cover the field with Depression (his AoE costs 3 AP and does relatively weak damage) – take SP-built Mary with him for “Seven years of bad luck” and then let him do his thing. Also, his Recharge, in correct circumstances and provided you are not fighting a “locking” battle, can allow you to set up fairly big turns.
Hecate: Her offensive build is about rapidly changing moon phases with 0-1 cost AP abilities, which builds up the effect of Cosmic skills, in addition to dealing plenty of damage on the way there. Best paired with Lilith and her relic that allows her to use her Recharge on other disciples – the Cosmic skills track Hecate recharging herself, not other characters recharging her, so they don’t get reset.