However a few do have "practical" uses - here are some examples: The particular card you reference, Garruk the Slayer, was created for the Magic 2015 prerelease and is used in a variant where one player plays normally and the other plays as Garruk
They happen as a result of some type of occlusion on the application rollers, resulting in an area of the card that is missing the varnish that is supposed to be there
While there are a handful of cards that synergize with the Wolf creature type, and even fewer that care if a creature is a Horror, there just isn't that critical mass necessary to make a tribe playable
Doubling up triggers for cards like Terror of the Peaks or Craterhoof Behemoth could easily help you close out a game
Master of Death Someone realized they couldnt make a zombified Squee, Goblin Nabob, since Squees immortal and all, so they made Master of Death instead