Uniy 2D Beat 'Em Up, how to do collision?

Hi there. I am currently working in a 2D beat 'em up using Unity 4.3 Native 2D tools. I am basing my game on Castle Crashers and I am completely stumped on how to do collision like they do. Any help will be much appreciated. Thank You.

If you want to stay 2D, I would define walkable Trigger-PolygonColliders.

Those Polygons also have walk vectors assigned to them, this way the game knows when I enter the stairs polygon and I press right, I actually go down the slope. The dark blue vector is the same for up/down.

If I walk off a polygon and not on another, I just fall, till I hit another polygon - this way you can let yourself fall off the ledge or the side of the stairs - you simply fall down till you hit another walkable polygon.

There are also Polygons that you can’t enter for stuff you need to go around, like the foot of the archway or the wall in the background.

For all of these collisions and triggers only small colliders(yellow dot) at the feet of the players are used, so they can walk up to a wall etc.

All things are drawn in layers based on their fake depth, so the archway is rendered in front of the players etc.

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