95% of the time, you'll want to use a STAB attack and build your set around that rather than just picking a handful of random attacks. The reason Genesect uses those three moves are because (1) it hits like a goddamn semi truck and (2) it beats a lot of very specific pokemon in OU right now
A powerful STAB is often nearly as good or better than a super-effective attack, and any difference in power is almost always made up for in versatility.
Anyway, if you're new, stick to analysis sets for your first handful of teams. Trust me.
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