Sort of like mocking Sotha then, huh?
I know this is not part of my first question, but I see that Mehrunes has fought Vivec and Alamexia each one time, how many times has Mehrunes came back?
Mehrunes fought Vivec, and Vivec saw that his foe was unarmed and offered him a silver longsword.
Mehrunes fought Almalexia and Sotha Sil over the ruins of Mournhold. The both of them managed to fight him off, but Almalexia was badly injured.
Mehrunes appeared in the Imperial City to destroy Martin Septim, but Akatosh sprang forth from Septim's blood mixed with the amulet of kings and vanquished the prince of destruction.
It's very possible he appeared other times too but those are not recorded in any of the books I've read. I do know that before the pact that Sotha Sil made with the Daedra in 2920, the Princes could be summoned into Tamriel much more easily, and before the First Era there was no barrier between realities at all, meaning Dagon likely stomped all over the world as he pleased.
edit: I don't count the events of Battlespire, because the player character fought him in his own hunting lodge, in Oblivion.