What Pokemon were revealed before their generation was announced?
Title, basically. There's lists of what pokemon were shown in the anime early before the anime moved to the relevant region, But I'm asking for cases like Bonsly (who was first revealed in XD in August 2005, but Diamond and Pearl were announced in 2006).
There was the statues of G4 Pokemon in Mystery Dungeon Red and Blue (Nov 2005) which featured Pokemon from G1-3 and after a quick check, Mystery Dungeon was released before Diamond and Pearl (Sept 2006)
So there's Lucario, Weavile, Mime Junior, and Bonsly revealed before their main game appearance.