Some flaws...

[SirSafir]

It is the dog, since in the notes the owner of the dogs CLEARLY states, that he found him eating other dogs (Dead dogs in the rooms), Hiding in the walls (The burrows of the wall), and since dogs are known to "Dig Holes" I wouldnt put any doubt it was Frisk.

The amabel thing, was discussed some many times on the forum. We have no idea what caused her to go under the crate. Heck It might just be in fact that amabel turned into a zombie.

As for the green blood, the dog was infected so as the monsters had green blood, i assume he did.