Legit aa

getgenv().Underground = true
getgenv().UndergroundAmount = 90

game:GetService("RunService").heartbeat:Connect(function()
    if getgenv().Underground ~= false then
    local vel = game.Players.LocalPlayer.Character.HumanoidRootPart.Velocity
    game.Players.LocalPlayer.Character.HumanoidRootPart.Velocity = Vector3.new(0,-         getgenv().UndergroundAmount,0)
    game:GetService("RunService").RenderStepped:Wait()
    game.Players.LocalPlayer.Character.HumanoidRootPart.Velocity = vel
    end
end)