In the anime and manga, there are three basic "Number" monster variants: Emperor's Key "Numbers" (monsters with numbers from 1 to 100), "Over-Hundred Numbers" (monsters with numbers from 101 to 107 that are not pieces of Astral's memory, but instead are the signature cards of the Seven Barian Emperors), and "Barian Numbers" (fake monsters created by Don Thousand)
Additionally, it requires your opponent to pay 500 LP to activate any cards or effects
Those who purchased them at their lows would have then sold them at their peak, making tons of profit in the process
These requirements have made trading near impossible, likely in an attempt to get players to buy booster packs instead
The full set contains 64 cards plus 12 AR, 10 SR, 5 SAR and 3 UR cards (Total of 94 cards in the set)
The best use case I can see with this is using it like a beefed-up No Rest for the Wicked, and instead of getting your stuff back to hand immediately, you make a bunch of tokens and then run out Illicit Masquerade