To get it "fairly" you need to unpack 4 cards of the rarest tier in the same set, aka an insane amount of luck/time which would be best used elsewhere.

Here's the method, since the game has an achievement required to edit the catch.gd in the game directory, I assume that's actually how you're supposed to get it. Open it and play the game. Open some pack then quit the game and paste the following code in the "cardsOpenList" section created by opening the packs ingame (just replace one existing).

{
"totalCardOpenValue": 40376,
"cardsOpened": [
{
"value": 94,
"totalValue": 10094,
"rarity": 7
},
{
"value": 94,
"totalValue": 10094,
"rarity": 7
},
{
"value": 94,
"totalValue": 10094,
"rarity": 7
},
{
"value": 94,
"totalValue": 10094,
"rarity": 7
}
]
}


Save it and launch the game : you should get the achievement (and the Holy Moly if you don't have it yet).