The easiest way to get this is to start the tutorial world on easy. As soon as you spawn, walk up the stairs in front of you and collect the bow and arrows situated right in front of you at the top. Next, gather 16 dirt blocks. Then, when night falls, get a skeleton to follow you to an area in-line with the staircase near the unfinished wooden hut. Trap the skeleton with a 2 dirt-high wall all around it & walk 50 squares away up the stairs. Aim your bow just above the skeletons head and fire away. Once the skeleton dies, the trophy is yours