The pair of Meld cards that create Urza Planeswalker are Urza, Lord Protector legendary creature, along with The Mightstone and Weakstone legendary Artifact
As there's only the one foil printing, shiny Claws of Gix have always been pretty pricey, at about $21, but a couple of copies just sold on TCGPlayer for $90
The best way to make sure your modular creatures die is to do it yourself
I hate having to play one-card answers like this, but if they're going to print a card that destroys Enchantments AND graveyards, I don't have Magic cards left if that spell resolves and I would prefer not to scoop to a dumb card
Plus, even if you don't manage to win the game on the spot, you're still throwing counters on your board every turn