To add to what Magnus is saying, visible target is very important, because otherwise the Avatar would have to move towards targets who cannot be seen because of some temporary line of sight blocker, such as the aforementioned vortex template. Since we've established that it won't move through such life threatening features, it also makes sense not to have do silly on field manoeuvres, such as curling a tape measure around the edge of a vortex template to move to unseen models behind.
Regarding the issue about adding the building caveat, I see no problem with including it as an example, but the key thing in this respect is to just the Avatar a unit type. If it says in rules that his unit type is infantry, by definition it can enter a building. Adding the note about the pinning class is necessary though.
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Soñando con una playa donde brilla el sol, un arco iris ilumina el cielo, y el mar espejea iridescentemente.
