Double-sleeving is particularly common in Commander, Cube, and older formats like Legacy and Vintage where it is not uncommon for many cards in your deck to be worth over $100 each
Always prioritize sold listings, especially on platforms like eBay, because they reflect true market demand, not just a seller's wishful thinking
C Common Mimikuril X DARK Level 3 [ FiendEffect ] ATK 0 DEF 0 During your Main Phase: You can excavate the top card of your Deck, and if it is a monster, Special Summon it, and if you do, place this card on the bottom of the Deck
It also meant that there was a potential price-crash-timebomb on Lord of the Rings Collector Boosters based on when the MTG One Ring was found, although even today they are holding decent value, mitigated in part due to other serialised cards found within them (The Sol Ring Rings of Power) and the sets general popularity and appeal to fans of both franchises