My Crap main.lua

local JokerMod = RegisterMod("Joker", 1)
local game = Game()
local MIN_FIRE_DELAY = 5

local GunId = {
    GUN = Isaac.GetItemByName("Gun")
}

local HasGun = {
    Gun = false
}

local GunBonus = {
    GunSize = 1.5
    GunSpeed = 2
    GunFireRate = 2
    GunDamage = 5
}

local function UpdateGun(player)
HasGun.Gun = player:HasCollectible(GunId.GUN)
end

function JokerMod:onPlayerInit(player)
    UpdateGun(player)
end

JokerMod:AddCallback(ModCallbacks.MC_POST_PLAYER_INIT, JokerMod.onPlayerInit)

JokerMod:AddCallback(ModCallbacks.MC_POST_PLAYER_INIT, JokerMod.onPlayerInit)

COSTUME_Joker = Isaac.GetCostumeIdByPath("gfx/characters/character_420_jokerHead.anm2")


--Applying Joker's costume
function JokerMod:PlayerCostume(player)
local player = Isaac.GetPlayer(0)
    if player:GetName() == "Joker" then
        player:AddNullCostume(COSTUME_Joker)
    end
end

local Joker = { -- Change Joker everywhere to match your character. No spaces!
    DAMAGE = 1, -- These are all relative to Isaac's base stats.
    SPEED = 2,
    SHOTSPEED = 3,
    TEARHEIGHT = 2,
    TEARFALLINGSPEED = 3,
    LUCK = 1.5,
    FLYING = false,
    TEARFLAG = 0, -- 0 is default
    TEARCOLOR = Color(1.0, 1.0, 1.0, 1.0, 0, 0, 0)  -- Color(1.0, 1.0, 1.0, 1.0, 0, 0, 0) is default
}

function Joker:onCache(player, cacheFlag) -- I do mean everywhere!

    if cacheFlag == CacheFlag.CACHE_DAMAGE then
        if player:HasCollectible(GunId.Gun) and not HasGun.Gun then
            if player.MaxFireDelay >= MIN_FIRE_DELAY - GunFireRate.GUN
                player.MaxFireDelay = player.MaxFireDelay + GunFireRate.GUN
            elseif player.MaxFireDelay >= MIN_FIRE_DELAY then
            player.MaxFireDelay = MIN_FIRE_DELAY
            end

            player.Damage = player.Damage + GunDamage.GUN

        end
    end

    if cacheFlag == CacheFlag.CACHE_SHOTSPEED then
        if player:HasCollectible(GunId.Gun) and not HasGun.Gun then
            player.ShotSpeed = player.ShotSpeed + GunSpeed.GUN
        end
    end

    if cacheFlag == CacheFlag.CACHE_TEARFLAG then
        if player:HasCollectible(GunId.Gun) and not HasGun.Gun then
            player.TearSize = player.TearSize - GunSize.GUN
        end
    end

end



--Removing any other costumes
function JokerMod:onUpdate(player)
    local player = Isaac.GetPlayer(0)
    if player:GetName() == "Joker" then
        if numocollect ~= player:GetCollectibleCount() then
        numocollect = player:GetCollectibleCount()
        player:ClearCostumes()
        player:AddNullCostume(COSTUME_Joker)
if game:GetFrameCount() == 1 then
    if player:GetName() == "Joker" then
            player:AddCollectible(GunId.Gun, 0, true)
        end
    end
end
        UpdateGun(player)

end
JokerMod:AddCallback(ModCallbacks.MC_POST_PEFFECT_UPDATE, JokerMod.onUpdate)
JokerMod:AddCallback(ModCallbacks.MC_POST_PLAYER_INIT, JokerMod.PlayerCostume)
JokerMod:AddCallback(ModCallbacks.MC_EVALUATE_CACHE, JokerMod.onCache)