too bad I'm rambling anyway
The Hounds of Tindalos appeared in a story titled as such by Frank Belknap Long, and later referenced by the big HPL himself. They are, in my opinion, amongst some of the best ideas to come out of the mythos... but they're symptomatic of a problem with a lot of early cosmic horror.
Namely the fact that the story itself is Not So Great.
Basically in it a man gets high to mentally travel through time and looks back too far. The Lines are horrible, and they committed some crime, represented through allegories throughout all the world's beliefs. As they travel through angles, rather than through space, they can move through time easily, but can be slowed by, say, rounding off corners so they cannot pass through them. They are immortal, and once they have your scent they will come inexorably for you.
I took some liberties in my depiction, but I tried to stay true to what I felt was the Feel of the Hounds.
You should play Sans because Sans is great.
Also speaking of Wynaut, does anyone want a Shiny one? I don't know how legal he is because he was the accidental end result of experimenting with a bunch of different Gameshark codes all at once and he's probably an abomination that's just a hair away from being a Bad EGG, but hey, purple!

just do what i do
keep spoilers disabled
UN JOUR JE SERAI DE RETOUR PRÈS DE TOI