How to make a block that slowly kills you after touching it?

Put this under the part that will kill

local killPart = script.Parent
local damage = 10 -- change this to how much damage to do

local debounce = true

killPart.Touched:Connect(function(part)
    if part.Parent:FindFirstChild("Humanoid") then
        debounce = false

        local hum = part.Parent:FindFirstChild("Humanoid") 

        hum:TakeDamage(damage)

        repeat wait() 
            killPart.TouchEnded:Connect(function()
                debounce = true
            end)
        until debounce
    end
end)

You could make use of the Touched event and then slowly damage the player after he hits it.

Eg :

local globalDeb = false

part.Touched:Connect(function(hit)
if hit.Parent:FindFirstChild('Humanoid') and not globalDeb then
globalDeb = true
repeat wait(0.8) hit.Parent.Humanoid:TakeDamage(10) until hit.Parent.Humanoid.Health <= 0
end
end)