Lifesteal game idea

How would I make it so when you get a kill your max health gets increased by one?
How would I make it so when you die your max health gets de-creased by one?

For the first one, you could do something like this

Health.Value += 1

How would I detect when you kill a player?

How do you want to kill players? With a sword, with a gun?

Not every tool are scripted the same, Fire the KilledBy function when someone gets killed, And also the script is from ServerScriptService

local Players = game:GetService("Players")

local HealthBar = 10 -- 
local MaxHealths = {}

local function SetMaxHealth(Character)
	local PlayerFrom = Players:GetPlayerFromCharacter(Character)
	local Humanoid = Character:WaitForChild("Humanoid")

	Humanoid.MaxHealth = MaxHealths[PlayerFrom]

local function KilledBy(Player, Killer)
	MaxHealths[Player] -= HealthBar

	if Killer then
		MaxHealths[Killer] += MaxHealths
	SetMaxHealth(Player.Character or Player.CharacterAdded:Wait())

	MaxHealths[Player] = 100
	SetMaxHealth(Player.Character or Player.CharacterAdded:Wait())

	MaxHealths[Player] = nil

Making a Lifesteal type game would be pretty simple concept, and not really that complicated to make, I’ll guide you through most of the steps.

When making this type of system, you have to take in the Amount of Damage the Humanoid has taken, when they die, and who killed them, do this with whatever weapon you are using whether its a gun, bomb, or just a Sword, for the Death system, we will look for a Tag called creator (we will need to create this Tag ourselves everytime a Player hits another Player) and then check its Value, creator should be an ObjectValue so we can store the Player inside it, so when we check, it will make our search much easier, in order to create this “Tag”, we would do this:

function spawnTag(Attacker, TargetHumanoid)
    -- Attacker Parameter is the Player who Attacked (The Player Instance)
    -- TargetHumanoid is the Humanoid whose taking Damage
    local creator ="ObjectValue") -- creates an ObjectValue
    creator.Name = "creator" -- the name of the ObjectValue
    creator.Value = Attacker -- Assigns the Value as the Attacker
    creator.Parent = TargetHumanoid -- places ObjectValue into our Target

But, this is just creating a Tag, there is no use for it at the moment, we need this Tag to work when the Player Dies, not just a random Accessory of the Player.

Before we Decide what to Grant the Player, we need to Decide whether the Player Killed Themselves (if you want that kind of system) or who Killed the Player, and you might be thinking: “Do we check for the ObjectValue??”, and you would be exactly right, we would check for it.

But before we do this, how would we check if they died? The Humanoid has a Event within it called Died which is exactly what it sounds, it fires when the Players Die, when the Player is Dead, we check for this Value using FindFirstChild to Avoid an Error for attempting index something nil, and if it finds the Tag, we grant that Player the Health, and the Player loses Health.

However if you want the Change to be permanent, you use a Value, maybe a IntValue to keep track of the Players Health, so when the Player dies, they dont get all their health back

    local Tag = Humanoid:FindFirstChild("creator") -- Value or nil
    local didPlayerDamage = (Tag ~= nil) -- This will return a boolean if there is a Tag
    if didPlayerDamage then -- if this Boolean is true
        local Killer = Tag.Value -- Gets the Player from Value
        Killer.HealthValue += 1 -- Adds to their Health
    Victim.HealthValue -= 1 -- Takes away from Player Health

I want to kill them with a sword

Dirbie90 what would I have to do to your script to make it work? where would I put it? THANKS!

Not wise to change the same variable inside of its own change event. Will cause infinite loop.