Not entirely sure if this was a coincidence, But this achievement unlocked on both versions (XB/W10) as soon as I unlocked my first hero. So try unlocking the first hero if you're having issues with the RNG aspect.
At any point during the game, but relies on RNG. Save up your leaves!
Easy, but random. On the first deck, gather up all the leaves you can, and click on the "boost" button on the right hand side of the screen. This will add a small boost to a random card's stats from your current deck, as signalled by a small sword icon in the corner of a card. Each card can have several of these.
Keep on clicking the boost until the RNG gives you four boosts on one card, and that's it!
This achievement can unlock even if you haven't gotten the card yet, as the boost can be applied to cards you haven't earned. So just click away until you get it.