Try this:
local monsters = {
name = "rat",
position = {x = 998, y = 1006, z = 7},
chance = 95 * 1000,
["alpha"] = SKULL_BLACK,
["trained"] = SKULL_RED,
["strong"] = SKULL_WHITE
}
function onThink(interval, lastExecution)
local chance = math.random(0, 100 * 1000)
if...