Mod as in "are you an Autobot or a Decepticon" related, I assume.
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from another post:
"There also appears to be four, count ‘em four, versions of this game. There’s the Pro edition and Limited Edition, but there will also be a Autobot (crimson) and Decepticon (violet) Limited Collector’s Edition for each. These Collector’s Editions will feature full cabinet trim in the versions color, unique backglass (of either Autobot or Decepticon), playfield-mounted "