Sorry about that :(
We're aware of this issue, the game was originally made in a week for a gamejam and we just didn't have enough time to balance enemies properly at the end. We're currently working on an update to make things fairer, but we will have to wait for the end of the voting process before pushing it live.
In case you want to give it another try without having to worry about that guy, here's a little secret: if you press SPACE+F you can take out an enemy in one-hit. This is not really a feature but just a developer option that wasn't remove for the live version, under normal circumstances we don't really encourage its use, but we feel like is an adecuate solution if you encounter this enemy too early, at least in the meantime. Now go get your revenge :)