Using GetDescendants to change a part property?

So im working on a tower of hell game and im now doing the mutators but i cant do the same mutators as tower of hell obviously, i already have the script of mutators working and etc but not the function, i wanna use the getDescendants to change the transparency of all parts in a folder to 0.5 what i tried to do is

--the mutators working script here

else if mutator.Name = XRay do
   for i, v in pairs(game.Workspace.Tower:GetDescendants()) do
      if v:IsA("BasePart") then
           v.Transparency = 0.5
      end
end

i dont know whats wrong with the script bc i rlly hate working with GetDescendants if anybody could help me it would be cool