I think he raises a good point. It's very well drawn, but if I were to see someone wearing this on the street I'm afraid I wouldn't be able to tell it was a Kelpie. If the kelpie were in action or appeared menacing, the 'mythical' message might come through a little clearer, otherwise people may confuse this with a regular horse. Still a good drawing though.
I can see that but there isn't really much else to the kelpie besides it looking like a wet horse. I could have added more elements to the design to hint it's a kelpie but I was afraid it would have gotten too complex to be a simple 5 color shirt design. I dunno I might think about it and maybe I'll enter another design of it.
I've seen a kelpie with tentacle-like things before, but it's up to you; it's still pretty early in the contest. The 5-color rule can feel limiting at times but it looks like you got a good handle on it with this color scheme.