Almost all engines can do that, so go for the one you're better at. If your game will use pixel art style, check if it supports nearest neighbor scaling (many do), so when scaling up or down you don't get blurry images.

If it's a fighting game (based on the name, it is), you can check engines like MUGEN or Kokusai Fighting Engine.

7 hours ago, Minifeg said:

So, I was wondering what is an relatively easy to use and flexible engine?

The whole point of using the pixel art is that there isn't a game engine that can't do it. It's the easiest art style to use and as such is very popular with indie developers.

Easiest engine would be Game maker, Unity is excellent for 2D games if you know how to program, Cocos2d is a fantastic 2D engine yet is a bit hard to learn, Unreal4 is good if you plan on making more than just 2D games; it's aimed at more experienced developers.

Godot. Great for 2D and open-source.