a skeleton

• 1055, 480, -51 (6 of 7 spawns here)
• 1086, 439, -48 (4 of 6 spawns here)
• 0, 0, 20313 (seen once) (4 of 29 spawns here)
• 0, 0, 20257 (seen once) (3 of 41 spawns here)
• 0, 0, 20282 (seen once) (2 of 17 spawns here)
• 931, -417, -51 (seen once)
• -884, 139, -51 (seen once)
• -670, 1188, -51 (seen once)
• 996, 1415, -40 (seen once)
• 827, 1556, -51 (seen once)
• 638, 3379, -51 (seen once) (1 of 2 spawns here)
• -656, 2781, -52 (seen once)
• -720, 445, -52 (seen once) (1 of 2 spawns here)
• 474, -1310, -52 (seen once)
• -740, 778, -52 (seen once)
• 694, 2008, -44 (seen once)
• 748, 2929, -52 (seen once)
• 862, 1888, -51 (seen once) (1 of 2 spawns here)
• 644, -1359, -52 (seen once) (1 of 2 spawns here)
• 793, 2353, -52 (seen once)
• -646, 1276, -51 (seen once) (1 of 2 spawns here)
• -612, 2562, -51 (seen once)
• 812, 2367, -51 (seen once)
• 1042, 1621, -51 (seen once)
• 851, 2577, -50 (seen once)
• -545, 2938, -51 (seen once)
• 577, 3331, -51 (seen once) (1 of 2 spawns here)
• 187, 3436, -51 (seen once)
• -139, 3460, -25 (seen once)
• -744, 88, -51 (seen once)

As /loc gives them: Y, X, Z, the most used first; nearby spawns share a spot, and one seen in a single visit may be where the mob had been pulled to.