I'm not familiar with Samhain as being a god or hero. It is the eve of Nov. 1, the first day of the new year and the first day of winter.
In the Celtic myths many unusual things happen on this night. It is a time between the old and the new and therefore an in between period where the borders between our world and the other world melt away. This was a solemn holiday, beings from the otherworld can find themselves in this world.
One story that illustrates this involves the hero Finn Mac Cumhall. Every Samhain some fire breathing monster would come and terrorize the castle of King Cormac Mac Art.
This otherworldly creature, named Aillin, had a harp that would lull the people to sleep so he can kill them. (I suppose this monster was more cultured than Grendel, at least he can play the harp).
Finn was a hero that was able to resist the sleepy sounds of the harp and was able to stay awake long enough to kill the beast.
So here we have a real type of Halloween story from the Celts illustrating what can manifest at Samhain.