black & white legendary treasures booster box B&W Pack Pokemon - Black and White

You can obtain the Gengar (3-Diamonds rarity) card by opening Genetic Apex: Mewtwo from Genetic Apex set

People can also alter cards in another way than just paint on them

PSE Prismatic Secret Rare Superheavy Samurai Swordmaster Musashi X EARTH Level 5 [ MachineSynchroEffect ] ATK 300 DEF 2300 1 Tuner + 1+ non-Tuner monsters When this card is Synchro Summoned: You can target 1 Machine monster in your GY

At the start of the Battle Phase: You can activate this effect

Once per battle, if this card battles, during damage calculation (in either player's turn): You can make this card's ATK and DEF become equal to the ATK of the monster on the field with the highest ATK (your choice, if tied)

The stolen monster then goes to the Graveyard at the end of the turn, but nothing is stopping you from using it as material before that