"10,000 Needles" isn't a real Magic: The Gathering keyword or ability—it doesn't appear on any official card or in the comprehensive rules. It sounds like a flavorful name, possibly confused with a video game attack (Final Fantasy's "1000 Needles") or a homebrew/custom card.
If you encountered this on a card, it's almost certainly an unofficial, fan-made, or joke card, which wouldn't be legal in sanctioned Commander play. Mythicwyrm or other custom-card platforms sometimes host community-designed cards with invented mechanics, so the rules text on the card itself would define what it does.
If you meant a genuine keyword—like Cascade, Deathtouch, Ward, or Myriad—let me know the correct name and I'll break down exactly how it works and why it matters in EDH.