With Oblivion being an open ended game, you can become the Daedric Prince of Madness and then do the Main quest. What's always struck me as odd, is, if you're going to save Tamriel, why do it alone when you have an army at your command? If the Mythic Dawn can summon Oblivion gates, why can't you, the Daedric Prince of Madness, summon gates as well?
The idea of two Daedric Princes clashing against each other in war has always appealed to me. And I thought it would be interesting if there was a spell that allowed you to summon your own gate. (Using Peryite's gate mesh would be nice.) that spawned Dark Seducers and Golden Saints to counteract Dagon's daedra.
See it like this.
You approach a gate, the deadra are spawning. In response, you summon your own gate that spawned Seducers and Saints that would fight alongside the imperial legion (If they're around) and battle Dagon's forces?
Why not show Dagon that if he wants Tamriel, he has to go through a fellow Daedra Prince? Summon Three gates of your own at the Battle of Bruma to negate Dagon's and make the battle easier. This would go great with the mods 'Daedra Overran Tamriel' and 'Enhanced Daedric Invasion' as you could aid these fellows by showing them they have Sheogorath himself aiding them.
Why stand up to Dagon as a lone Hero? Why not as Sheogorath, let him know you aren't going to stand by and let his invasion succeed?
Just a request,
ZaWarudo.
This IS possible. Summon Oblivion Gates allows you to summon Dagon's Oblivion gates and gives you a spell to destroy them.
