these are known as Enchanted cards, and we have an example of one of these cards in the image above, which shows the Enchanted Stitch card, from Disney Lorcanas The First Chapter set
This card screams build around me in a control shell and gives you massive flexibility, especially if youre ramping or dealing damage along the way
If Primeval Spawn would enter the battlefield and it wasnt cast or no mana was spent to cast it, exile it instead makes it so you cant Reanimate, Sneak Attack or Polymorph it into existence and this design choice feels very deliberate
A single discard effect will rarely inflict devastating damage, unless your opponent doesnt know the worth of their own cards
To make this chaotic machine run smoothly, youll need cost reducers like Etherium Sculptor, card advantage from Mystic Forge, and a way to win like Aetherflux Reservoir