Galaxy 2 should be able to put up comparable numbers to the first one (7-8 million) by just releasing it with a decent advertising campaign. But Nintendo can really make it a big deal if they stretch that advertising and try to get it to the more casual and new gamer crowd... something they have struggled to do with 3D Mario. Even further attempt to get Japanese gamers involved more heavily in it (I mean NSMB Wii outsold Galaxy in 2 weeks of sales in Japan). If they are really big on advertising and associating it as the next big Mario game after NSMB Wii (possibly lowering the price of Galaxy 1 with incentive beforehand) they push this game to being a 10 million seller as well.
But that's going to be hard to do but Nintendo does have some very large and effective marketing campaigns they run.
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