It attacks players at night when they're in the new biome, the pale garden (which also has an awesome wood type that totally goes with decked out). You can only defeat them by mining their heart, which can easily be picked up with silk touch. They will only attack you when your close up to them, or aren't watching them. Its design is also super cool imo! I think Mojang did an awesome job with the new update, although I saw a bunch of people who were sad there wasn't anything new for the end.
