So here's what I came up with. The idea is that Fort can use one barrier to "burrow" a target creature. That creature can no longer be targeted by CC just like with burrow, as long as as Fort/Castle still has barriers left. The opponent would have to use PC on Castle, only removing one barrier at a time. If more than one creature is sheltered and there is an equal amount of barriers left when PC is used on Fort/Castle, a barrier is removed as usual and the last creature to be sheltered loses its protection.
I think it fits Earth pretty well considering its defensive nature and use of "burrow". I'm not sure about whether or not it should stack, which wouldn't matter at all except when using PA, which could make a very powerful combo. This is one of the many things I want your opinions on, that is(obviously) why I'm posting this thread. Other quite uncertain attributes are card/skill cost, amount of barriers and other things that require expertise and balancing.
Also, if anyone wants to do artwork for this, that would be very welcome. I'm not going to lie, the picture is straight from google
, though I think it fits pretty well.
So, all comments and critique welcome and encouraged