This card already exists. It’s just not collectible.
https://hearthstone.gamepedia.com/Vaelastrasz
Yes, I would also like to play with such crazy cards in a custom game format.
A spell I would like to see that you can play (in such a custom game mode) would be like this: “Portal to Infinity, 10 mana, Replace your deck with an endless source of random cards” (legendary mage spell) Now that would be awesome! What do you think?