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I would caution the reader that the trading value of a card is not necessarily a good predictor of in-game power, as some people totally misunderstand the game mechanics and pay way too much or too little for the cards. I would also caution you not to assume a banned or restricted card to be better than a non-banned or non-restricted card, as even the game developer does not know how to rate cards properly sometimes.
Mana Drain
Static Orb
Vengeful Dreams
Force of Will
Nostalgic Dreams
Fact or Fiction
Life Burst
AI Opinion
Magic: The Gathering has so many powerful cards, but the one that stands out from your list is Force of Will. It’s practically a staple in many formats due to its incredible ability to counter any spell without leaving you defenseless by tapping out. The fact that you can cast it for free by merely exiling a blue card and paying one life makes it extremely versatile and a lifesaver in many situations. Even though it's pricey, the utility it provides in maintaining board control is unparalleled. Just seeing Force of Will in someone’s deck often strikes fear because it means they always have an answer up their sleeve! 🃏✨
I'll wait until a few posters reply and vote before giving my opinion of which of these cards is most powerful overall and why.
There's an argument for everything. I don't think Life Burst is the strongest of these 7, but I do think Life Burst needs erata and converted to a Sorcery card, because gaining as much as 16 to 32 or more life (free for all formats) for as little as 2 mana is absurdly overpowered. It doesn't effect EDH where you are limited to only one copy of a card anyway, but in Standard and Modern, when Life Burst rotates in, it is game breaking, which is why I put it on this list of 7 cards.
The real reason I put Life Burst on the list is because as an Instant, it combos perfectly with Isochron Scepter, and it forces your opponent to commit to all-in attacking you. If you are playing Prison, you then play your board-wipe card and wipe out your opponent's entire army, which if they never drew their disenchantment card, then they have been forced to over-commit to attacking and are baited into a Wrath of God or other board wipe.
Force of Will is not even necessarily the best "free" counterspell anymore. In some situations, Foil is more powerful. In other situations, Pact of Negation is more powerful. I put it on this list just to see how people would respond.
You can re-read the list and change your mind if you like, or you can stand by your original statements. LOL. When you see my arguments for and against each card, you'll understand.
Nostalgic Dreams is the most powerful of those 7 cards. In the middle and late game, you can hold one counter and one Nostalgic Dreams and hold 5 extra lands. Then cast Nostalgic Dreams and get back 5 used cards from the graveyard, including any 5 cards from this list of 7, making it literally X times more powerful than any of the other cards among these 7.