How We Roll Winner
He didn't technically say he was here at the moment of creation, he said he was present before the other elements were brought together.
But pure darkness, is in and of itself, an element too. It could be he was speaking metaphorically and referring to a void or an abyss possibly.
Smudd never killed Sepulchure, A tail coming down and squashing you (especially a tail that big) is aided by gravity. What might look like force to us due to the cutscene, may have been just gravity assisting the movement.
sure it was quick. But than again, the battle-attacks of the smudd were rather quick and quite hurtful as well. Especially if you didn't have the doomknight class helping you to battle.
The doom blade never stated that Sepulchure had to follow it's orders. It was relaying information to him. Sort of like a second conscience, much like xing and xang.
And it never really implied who the master actually was. Sure the Mysterious Stranger is involved and was selling doom weapons, and that the darkness of the NBOD went back up into a shape and disappeared into the mysterious strangers arm, but that doesn't really mean the MS was the master Sepulchure followed.
It's very possible, sure. And there's a lot of evidence to support the theory, but there's also doubts. Sepulchure and Drakath were both defeated. That much is true. But look what transpired to Drakath at the ending cutscene. Look what we witnessed at the ending cutscene for Seppy.
If you want my opinion, we haven't seen the last of either of them, and we've probably not seen the last of the MS either.