This foil Karn was only given out to Top 32 players at the Pro Tour
The Dragon potentially comes down for as little as three mana, and allows you to convoke any spells being cast from exile, not just the card you tutored
X=1 is pretty bad, X=2 is serviceable, and anything from X=3 and up seems actively strong
In my opinion, the strongest things you can do in Mono Red are: "Glass cannon" decks that either quickly pop off and win before opponents can stabilize, like Storm, Krenko, Purphoros, Slicer Crushing nonbasic lands, aka defeating a large chunk of players with a single Blood Moon The problem with these two strengths is that they aren't always the right pick for casual tables
These are cards that have spiked up in value over the past year or so because of the popularity of Old School and the changing collectible marketplace