No. The mudskipper does NOT so appear. It has fins, not feet. It has none of the amphibian skull anatomy of Tiktaalik or other genuine transitional candidates. Etc. And of course as a living creature, with no indication of a long fossil history, the mudskipper is not properly positioned in time to be a transitional, even ignoring its anatomical unsuitability.
I am not trying to pick a fight but do you really have knowledge of the fossil history of the mudskipper?
Respectfully, this isn't a very good answer. Notice that the mudskipper has little legs with feet in the front and is mobile out of water. Also, are you saying that it can't be transitional because it's alive? At what point do you determine that something is "done" "evolving?"