Torso is not a valid member of Model "Workspace.SCP-087-D" server script?

It's probably because the SCP is R15. Also next time, fix your answer, you should always put your code inside a code block by pressing the Lua icon. And provide some details on what you're trying to do and explain why you're doing this.

The solution is using script.Parent.HumanoidRootPart instead of script.Parent.Torso.

local monster = script.Parent
local monsterTorso = monster:FindFirstChild("Torso") or monster:FindFirstChild("HumanoidRootPart")

function findNearestTorso(pos)
    local list = game.Workspace:GetDescendants()
    local torso = nil
    local dist = 30 --This Line Right Here

    for _, descendant in ipairs(list) do
        if descendant:IsA("Model") and descendant ~= monster then
            local temp = descendant:FindFirstChild("Torso") or descendant:FindFirstChild("HumanoidRootPart")
            local human = descendant:FindFirstChildOfClass("Humanoid")
            local Friend = descendant:FindFirstChild("Friend")
            if (temp ~= nil) and (human ~= nil) and (human.Health > 0) then
                if Friend ~= nil then
                    if Friend:IsA(monster.Friend.ClassName) then
                        if Friend.Value ~= monster.Friend.Value then
                            if (temp.Position - pos).Magnitude < dist then
                                torso = temp
                                dist = (temp.Position - pos).Magnitude
                            end
                        end
                    end
                else
                    if (temp.Position - pos).Magnitude < dist then
                        torso = temp
                        dist = (temp.Position - pos).Magnitude
                    end
                end
            end
        end
    end

    return torso
end

while true do
    task.wait(0.1)

    local target = findNearestTorso(monsterTorso.Position)
    if target ~= nil then
        script.Parent.SCP:MoveTo(target.Position, target)
    end
end