are there any free 2d level editors for unity? are they internal, external (i mean if I have to import the level as an asset).
What do you exactly mean by 2D level editor ?
You can either do it in a 3D package (maya,3dsmax blender, etc…) and import the level in Unity or you can do it directly in Unity. If you are looking for a tool to help you place and align your props on screen for 2D games, I don’t really know one. However, it should not be hard to code it yourself if that is what you are looking for.
i meant like a drag n drop tiled editor, I saw how difficult it was to make a 2D game by scratch, so I was wondering was there a tool, but if not, how would I make it in blender?
Try this one its free but it doesn’t do tiles I think :
http://forum.unity3d.com/threads/128965-fg2D.-A-free-and-open-source-2D-solution
another free one: http://forum.unity3d.com/threads/95827-Orthello-2D-Framework-100-FREE
This one is free, has a tile mapper and is drag and drop :
Non-free ones:
http://forum.unity3d.com/threads/72934-UniTile-2d-Tile-based-Map-Editor-within-Unity
http://forum.unity3d.com/threads/93287-2D-Toolkit-2D-in-Unity-made-simple-RELEASED
http://forum.unity3d.com/threads/124211-Smooth-Moves-2D-Skeletal-Animation
This one is tiled-base but not 2D, but could work in a 2.5D game :
http://forum.unity3d.com/threads/120326-Tidy-Tile-Mapper-Paint-tile-maps-from-the-Editor-Released
Doing it with an editor is easier and they usually provide a Sprite Atlas tools so it can combine the textures you are using into one or more bigger texture to save Drawcalls. They also provide many tools for animation, tiling or other stuff.
If you want to do it in blender, you have to model your level inside blender using quads for the sprites but you need to keep in mind what texture is used and where in your game, so you can make your own atlas. Then you need to UV map your level and export to Unity.
There are various way to animate the characters in 2D, one is by scrolling through a texture and there are many tools for that. Another way to animate the characters (if he is made of many quads) is to use Blender or there is an equivalent tool for Unity called Smooth moves 2D skeletal animation (I give the link above).
You might be interested in below tools
A very education tutorial on how to use them can be found on YouTube
and unitys own coming 2d tools,
If you want to start with something already completed (source code included!), you should check out this
It handle animated tiles, multiple levels, walls, teleports and many more!