Every living thing has a way to reproduce. The 'genderless' tag on Pokemon in the games is to prevent players from breeding legendary Pokemon. That way, unless you traded (or cheated), you could not have more than one as it would contradict with the game lore.
However, even in the anime it is shown that legendary Pokemon have the ability to reproduce and have young.
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ARCEUS
Arceus.
arceus
yes arceus can learn HM fly, because i have a arceus and i have taught it HM fly
yes you can get arceus on any sinnoh game