User blog comment:KillRoy231/Will we ever see Asmodeus?/@comment-1031724-20170521061958

Sam and Dean need a new demonic ally. They had three in the past and they're all dead:

Now, let's take a look at the archetypes of the Princes of Hell:
 * 1) Ruby - Seasons 3 and 4, revealed to be evil and killed by Dean
 * 2) Crowley - Season 5, revealed to be evil in Season 6, semi-reforms in Season 9, on and off ally until his final redemption and death in Season 12
 * 3) Meg - Joins Sam and Dean's side in Season 7, killed by Crowley in Season 8

Asmodeus lost interest in Lucifer's cause. So did Ramiel and Dagon, but Ramiel was still an antagonist in his own way, and Dagon rejoined Lucifer. So, what if Asmodeus becomes a Winchester ally, even if he could be a not-always-reliable one, as a replacement for Crowley coz his death seemed final. (They need to get someone really fun to play Asmodeus if he can hope to replace Crowley)
 * 1) Azazel - Main villain. Of two seasons
 * 2) Ramiel - Monster of the week
 * 3) Dagon - Secondary antagonist of a season, as she is working for Lucifer and lasts quite a few episodes (though way less than Ketch)