Gill makes sense because he's a broken boss-character, and system only characters also make sense because tournaments could then come down to what system it's being played on and that's not fair to an entire community. I honestly have no idea about the Tekken thing though.
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Official Board 8 Brawl and Pokemon Champion
http://images4.wikia.nocookie.net/board8/images/8/8b/ViviffChampS1.jpg