a shoal serpent

• 257, 42, 85 (2 of 5 spawns here)
• 375, -865, -306
• -353, -929, 122 (seen once)
• -481, -86, -32 (seen once)
• -934, -2137, 159 (seen once)
• -143, 181, -7 (seen once)
• -400, -147, -9 (seen once)
• -737, 406, 109 (seen once)
• 47, 439, 21 (seen once)
• -480, 42, -84 (seen once)
• 292, -1744, -137 (seen once)
• 65, -1327, -116 (seen once)
• -723, 333, 72 (seen once) (1 of 3 spawns here)
• 767, -1439, -11 (seen once)
• -997, -554, -186 (seen once)
• -96, -87, -38 (seen once)
• 520, 157, 45 (seen once)
• 164, -1275, -13 (seen once)
• 601, 548, 219 (seen once)
• -790, -1270, -64 (seen once)
• -42, 439, 52 (seen once)
• -173, -1743, -346 (seen once) (1 of 2 spawns here)
• 980, -591, 139 (seen once)
• 421, -934, -8 (seen once)
• -629, -1902, 68 (seen once)
• 65, -1328, -76 (seen once)
• -978, 93, -62 (seen once)
• -73, 265, 24 (seen once)
• 490, 148, 61 (seen once)
• -599, -955, 4 (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.