Supernatural: Every Major Villain Ranked Worst To Best
3. God
Throughout the show the Winchesters faced varying levels of angels and demons, it only made sense to end with God himself.
Known commonly as his vessel "Chuck", God had played a major role through the entirety of the show whether it was due to their absence or meddling. As it turns out, God had been trying to get Dean and Sam to kill each other for some time, allowing demons and other entities to run amock to do the dirty work for him.
Much like the old biblical tales, Chuck is a vengeful and merciless God. Any and all hardships that befell the Winchesters was caused either directly or indirectly by Chuck. This was all due to Chuck's plan of creating a good "story" as a sort of metacommentary from the showrunners.
In the end, God even offers up multiple ending for Sam and Dean to choose from with the two refusing and choosing their own destiny for once.