They are pretty good in decks in a format that goes long
And if you decide its not your style, thats fine too
He's an eight-mana 5/5 with flying that allows you to cast cards from the top of your library equal to the total power of attacking wraiths
First and foremost, Stoneforge Mystic is in Modern, and Stoneforge Mystic decks will be able to run it as a one-of, hope it hangs out undrawn in their library in matchups where it is bad but find it consistently with Stoneforge Mystic in matchups where it is good
Its ability reads, Whenever a land enters the battlefield under an opponents control, that player exiles the top two cards of their library, and you draw two cards. Were not sure about your playground, but in ours, people like to be able to play Land cards
Then the rest go to the bottom of your library to draw, but that's just lands and not likely to be many