As a reminder, when you craft or open a booster containing a card rebalanced for Alchemy, you will receive both the Standard and the Alchemy version of the set
Gas Guzzler offers a cheap Vampire body that can effectively function as another copy of Skullclamp once youve reached max speed by turning small bodies sideways in the early turns and draining opponents with creatures such as Blood Artist
Well, I like to just pick the card back up (likely from the graveyard) and just keep on re-triggering the ability till my opponents buy what Garys selling
Getting your cards graded is a great way to help the selling process go smoothly and it can give you a better understanding of how rare and valuable your card is, too.
Theres Zaxara, the Exemplary and Magus Lucea Kane as the two most popular X-spell commanders, with Rosheen Meanderer as something a bit more niche
For reference, a Special Illustration Rare lands around 1 in 90 packs, an Ultra Rare around 1 in 15, an Illustration Rare around 1 in 12, and a Double Rare around 1 in 5