Nyarlathotep
Eldritch Abomination
A lot of the Mega evolutions are ugly to be honest (Manectric comes to mind). The selection process was a bit weird too (Manectric comes to mind again). Some pokemon that got them honestly should have gotten proper evolutions instead (Mawile, Absol).
Good thing ugliness is subjective. What you find ugly, other people might find pretty and cool. I don't see much difference between mega evolutions and "proper" evolutions. They are all evolutions, except one is temporary and has a freaking cool evolution animation during battles (seriously, my Mawile is like a Kamen Rider transforming every time he goes to battle ). Also, one can say that a lot of proper evolutions are ugly as well. Rhyperior, for example, is commonly said to be ugly... I don't agree though, I think it looks awesome. Magmortar, on other hand.... Ew. Seriously, I am all for more mega evolutions instead of proper evolutions. The dex is already monstrously huge, so I'd rather Game Freak create evolutions that aren't counted in the dex, like megas. Plus, as I said, the in battle transformations are freaking cool.