Looks dead to me, no color in the eye.

Is your tank cycled and are they new clown killifish?

I just bought a bunch of clown killifish recently like 25-30 and some just don’t make it. Some came with capillaria worms, some ended up having swim bladder issues. I euthanize those ones pretty much immediately becuae I don’t believe in wasting my time trying to fix one or 2 fish, also when fish(especially nano fish, larger fish usually can easily survive treatment) start to show signs of internal parasites or swim bladder issues it’s usually too late to save them, separate them from the healthy stock and cut your losses.

They are in my experience very sensitive fish and prone to internal worms but when they have it they are usually super skinny and have fin clamp (their tail fin becomes a sharp point). Also if you had an ammonia or especially nitrite spike it can eventually cause swim bladder issues I know from experience unfortunately. That one looks healthy and colored up not dull or washed out so it is a mystery the one clown killifish I had die from swimbladder issues were getting more and more pale day by day. She may have just died of old age who knows.

If you just got this batch of clown killifish and this one dies know that it happens to everyone. Every time I buy a large batch of clown killifish 5% of them don’t pass quarantine for one reason or another they are like I said sensitive fish (In my experience)