RFTools Shield Projector
RFTools implements a 'simple' shield system that can filter mobs, animals, players, and items. You start by building the shape of your shield with connected Shield Template Blocks. Then you put a Shield Block next to one of these templates and you give it power.
By default there is a maximum of 256 blocks in a single shield. There is also a tier 2 shield that can do up to 1024 blocks. The tier 3 shield does more damage and uses more power.
To compose the shield you then need to right click the shield block with a wrench. The shield block will compose the shield in the specified shape. Wrenching the shield block again will turn the shield back into the template blocks. By doing that you can change the shape of your shield in case you're not happy with it.
Craft a Shield Projector with the following recipe:
Here is a screenshot of the user interface:
Showing the Wither being contained in a shield:
