A villain unlike any other is granted a body weak enough to be killed by the wind. But he will cause mayhem, no matter his size! Armed with skills allowing him to create more mosquitos which he can control and the ability to evolve and raise his stats, he will surely cause destruction never before seen! Though, as it turns out, living as a mosquito in a city might be a bit harder than previously thought. Especially so when super-heroes pop up out of nowhere. 

In short, a villainous man who really wants to destroy everything and anything he can is turned into a mosquito by powers beyond him. His powers, being that of evolution and stat-increasing, combined with his power to create more mosquitos, will eventually lead to him becoming just like... a swarming mass of mosquitos. 

Isekai reincarnated as a monster fic x villain in a superhero world fic