HeavyMetaldramon was introduced in the Digimon Liberator webcomic, and it quickly became a fan-favorite, alongside its Tamer, Yuuki
This is because you can select cards in your Graveyard that can return to the Extra Deck (for example, Synchro Monsters), so there is no guarantee on at least 2 cards being returned to your Deck at the end when Pot of Avarice's second effect (drawing 2 cards) resolves
The cards are first protected by an inner sleeve thats barely larger than a standard card, and then insert the card/inner sleeve inside a regular gaming card sleeve
In fact, about a month later, I took it apart completely and built a different Vintage deck
Gaea's Blessing : Whenever a spell you play is countered, draw a card
is another option for ebay