Hello !
Sometimes, I have a HUGE wraith generation that sometimes even make my game crash. Spawns like 40+ wraith 
.
Hard to tell what’s happening, my guess would be that when I use Sacrifice (with the node that propagate at all minions around, Catalyst of Horror), each explosion is considered as the killer of the monster so each Sacrifice explosion can trigger on each monster the chance to spawn a wraith.
So basically if I sacrifice 10 minions --> 10 explosions --> 20 monsters killed --> each explosion considered as the killer so 20x10 = 200 kills considered --> 200x0.25 = 50 wraiths spawned. This is my guess, maybe you can confirm !