Anyone can do that, so your opponents in a multiplayer game will happily attack each other for cards, and they might even let some through to draw more cards
The supply of cards on the secondary market (stores, social media groups, p2p trading, marketplaces) obviously depends on in-game rarity
Fable Flute lets you look at the top 5 cards from your opponents deck and bench any Basic Pokmon you find there, thats a great way to disrupt your opponents bench with cards like Lumineon V and it may also give you a target to Boss up and easily KO
Four massive legendary Eldrazi are included for use as a Commmander of your choice
When sleeves (or other storage products) state "standard size", it is typically referring to this 63 by 88 mm specification
You can only sell cards if you have 3 or more of them