The reason Sheik, Jiggs and Ness are still kept are because of seniority in two cases, a really well done moveset that become extremely popular in Melee and by now has a lot of followers and the love of Sakurai for Earthbound / Mother and do not forget that Jiggs still has one of the more unique and wacky movesets from all the cast that by now has a huge following and no one can replicate. Compared to Lucario that has one of the blandest movesets, a broken mechanic, not a lot of people used it compared to others and a huge competition in his own series from all 719 critters, puts him in a really rough spot especially because the game needs a balance between all the series that are in Smash, the same reason we don´t have 10 characters from Mario Series, or 5 lords in Fire Emblem, there still need a balance.
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