Hmm, they told me it was a tetra at the pet store, but considering how little it looks like a tetra, they could have been wrong.
Here's another photo of it:
If it's a killifish, should it get along with my others? I have a snakeskin guppy, a pearl gourami, a black widow tetra, a swordtail, a pleco, a blue ram, a diamond tetra, and an x-ray tetra.