a lowland basilisk

• -1810, -2565, 8
• -1864, -2701, 3
• -1562, 208, 3 (seen once)
• -1787, -628, 3 (seen once) (1 of 5 spawns here)
• -1708, -630, 9 (seen once) (1 of 3 spawns here)
• -558, -1034, 6 (seen once)
• -673, -2514, 3 (seen once)
• -450, 125, -25 (seen once) (1 of 3 spawns here)
• -2376, -354, 4 (seen once)
• -1570, -404, 3 (seen once) (1 of 2 spawns here)
• -2054, -624, 4 (seen once)
• -1405, -550, 20 (seen once)
• -4, 327, 3 (seen once) (1 of 3 spawns here)
• -1332, -1118, 5 (seen once)
• -1214, -1732, 3 (seen once)
• -832, -1973, 15 (seen once)
• -156, -2041, 3 (seen once) (1 of 5 spawns here)
• -1948, -2644, 3 (seen once) (1 of 3 spawns here)
• -1723, -485, 3 (seen once)
• -1524, -964, 2 (seen once) (1 of 3 spawns here)
• -1681, -1172, 3 (seen once)
• -1461, -1597, -5 (seen once)
• -1415, -2217, 3 (seen once)
• -442, 423, 3 (seen once)
• -1098, -899, 16 (seen once) (1 of 8 spawns here)
• -1526, -993, 2 (seen once) (1 of 3 spawns here)
• -1279, -2267, -32 (seen once)
• -1558, -1659, 3 (seen once) (1 of 6 spawns here)
• -2556, -1828, 5 (seen once) (1 of 2 spawns here)
• -1261, 382, 3 (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.