You can not get him while playing a game. I believe there will be a wifi event in which he will be given.
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you use action replay dsi to catch genesect(genesekuto)
You'll need to wait for a Mystery Gift event for the future to get Genesect. In Japan they still haven't got Genesect. So, it maybe awhile.
You get Genesect by event. You can probably get it at Gamestop... Hope this Helped :)
At this time, there is no legit way to capture him.
the Pokemon name that is ripped says genesect