How come players in my game don't die when they reach 0 health?

Your problem could be in several factors.

• You don't check the player's health correctly

• You don't subtract the player's health correctly

How do you check if the player's health is less that 0? If your using

if humanoid.Health == 0 then whatever end

then you are doing it wrong. You need

if humanoid.Health <= 0 then whatever end

However, I doupt that this is your problem. Now, I bet you damage the players via the following method:

humanoid.Health = humanoid.Health - 20 (or whatever the damage is) end

While this is not wrong, it is also possible to do it via the :TakeDamage() function. your script would look like this:

local damage = 20 --How much damage the knife does
humanoid:TakeDamage(damage)

Lastly, if all else fails, I have only one idea of what to do. Check it the player has <= 0 health, and then call the :LoadCharacter() function on their player (not character). Your script would look like this: (LocalScript inside StarterPlayerScripts)

local player = game.Players.LocalPlayer

while true do wait(0.1)
    if player.Character ~= nil then
        local humanoid = player.Character:FindFirstChild('Humanoid')
        if humanoid ~= nil then
            if humanoid.Health <= 0 then
                humanoid:TakeDamage(math.huge()) --Makes them take infinite damage. (Might not work in your case)
                player:LoadCharacter() --Forces them to respawn
            end
        end
    end
end

Accept if helped thx