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The Pokémon World Tournament had all Gym Leaders and Champions, but no Elite Four members.
Ethan, Lyra, Silver, Will, and Karen last appeared in HGSS (2009). Dawn and Lucas also count if you count their sprites being present in multiplayer. Palmer, Thorton, Dahlia, Darach, and Argenta also last appear here.
Aaron, Bertha, Flint, and Lucian last appeared in Platinum (2008).
Scott, Noland, Tucker, Spenser, Brandon, Lucy, and Greta last appeared in Emerald (2004).
Kris last appeared in Crystal (2000).