```lua
local Players = game:GetService("Players")
local RunService = game:GetService("RunService")

local Thing = {}
Thing.__index = Thing

function Thing.new(instance)
    return setmetatable({instance = instance}, Thing)
end

local fire = Instance.new("Fire")
fire.Size = 8
fire.Enabled = false

local PlayerCharacter = {}
PlayerCharacter.__index = PlayerCharacter
setmetatable(PlayerCharacter, Thing)
PlayerCharacter.EXTINGUISH_TIME = 5

function PlayerCharacter.new(model)
    local self = setmetatable(Thing.new(model), PlayerCharacter)

    self.isOnFire = false

    self.fire = fire:Clone()
    self.fire.Parent = self.instance.PrimaryPart

    self.extinguishTimer = 0

    return self
end

function PlayerCharacter:setOnFire(onFire)
    if onFire ~= self.isOnFire then
        self.isOnFire = onFire
        self.fire.Enabled = onFire
    end
end

function PlayerCharacter:update(deltaTime)
    if self.isOnFire then
        self.instance.Humanoid:TakeDamage(5 * deltaTime)

        self.extinguishTimer += deltaTime
        if self.extinguishTimer >= PlayerCharacter.EXTINGUISH_TIME then
            self:setOnFire(false)
            self.extinguishTimer -= PlayerCharacter.EXTINGUISH_TIME
        end
    end
end

type PlayerCharacter = typeof(PlayerCharacter.new(Instance.new("Player")))

local Game = {}
Game.__index = Game

function Game.new()
    local self = setmetatable({}, Game)

    self.things = {}
    self.updatingThings = {}

    for _,player in pairs(Players:GetPlayers()) do
        local character = player.Character
        if character then
            self:addPlayerCharacter(character)
        end
    end

    Players.PlayerAdded:Connect(function(player)
        player.CharacterAppearanceLoaded:Connect(function(character)
            self:addPlayerCharacter(character)
        end)
    end)

    RunService.Heartbeat:Connect(function(deltaTime)
        for _, updatingThing in pairs(self.updatingThings) do
            updatingThing:update(deltaTime)
        end
    end)

    return self
end

function Game:addPlayerCharacter(character)
    local playerCharacter = PlayerCharacter.new(character)

    self:addThing(playerCharacter, character)
end

function Game:addThing(thing, instance)
    self.things[instance] = thing

    if thing["update"] and type(thing["update"]) == "function" then
        self.updatingThings[instance] = thing
    end

    instance:GetPropertyChangedSignal("Parent"):Connect(function()
        if instance.Parent == nil and self.things[instance] then
            self.things[instance] = nil
            self.updatingThings[instance] = nil
            instance:Destroy()
        end
    end)
end

function Game:update(deltaTime)
    for thing in pairs(self.things) do
        thing:update(deltaTime)
    end
end

local myGame = Game.new()

task.delay(4, function()
    local me = myGame.things[Players:GetPlayers()[1].Character]
    me:setOnFire(true)
end)
```