How do you make MT_TAILSOVERLAY have transparency and fullbright?

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this is how i am trying to do it, but it doesn't work
addHook("MobjThinker", function(Tails)
if player.mo.skin == "stealth"
local Tails = MT_TAILSOVERLAY
Tails.frame = $1 | FF_FULLBRIGHT | FF_TRANS60
end
end)
please tell me what im doing wrong, although idk if anyone has tried this because there is almost nothing on this.