You could just get one-star yu-gi-oh card and boom, you've got a 1000/1000 that you can play without tapping anything. Unless your opponent has removal or something, you're winning as soon as it can attack
In Magic, if a card doesn't have a mana cost, it cannot be cast by normal means. Since you only get add the outside card to your hand, not put it into play, you now have absolutely no way of playing it. That 1000/1000 is stuck in your hand.
You can only have four of any card in most Magic formats. So even with perfect draws, you're only getting four pieces of Exodia, without retrieving this from a graveyard. Theoretically doable, but in Magic any deck that relied on playing the same card five times would be a genuinely terrible deck.
The real issue isn't that the card would have a way to cast it there's in game ways around that with stuff like cascade.
So assuming you have a way to cast a card with no mana value whatever card would go on the stack and do nothing then just enter your graveyard, probably. That being said I'm no judge.
Cascade would require the card to go into your deck, not your hand. More likely you'd have to get into your graveyard using something like dredge or One With Nothing, and then use some kind of resurrection spell to put it in play. But then you'd have to deal with the fact that most resurrection spells target a specific type, like "creature".
What’s the consensus on the rules of the game for the chosen card?
Would a Cards Against Humanity black card, which does not require mana to play, be playable? Would other players have to ‘respond’ with a card from their hand?
If you get multiple of these (or recall from graveyard) can you play the card if you also bring in the activation mana/cost whatever?
Is mana equitable across games? If you pull a card from a game that uses the same color mana as your deck, can you play the card? (For example, the game Not Enough Mana uses blue mana that is represented by a water drop.)
We OG players asked all these questions with the Ring of Ma'rûf
And yes, you can get any card (say a Jyhad vampire) into your hand, but we hadn't figured out how to get it into play.
A clever use for it at the time was to bring in a powerful but reasonable custom made card (preferably one with novel, interesting effects) and then cast that. This was especially cool at the time since this was before Tempest. Power creep was not yet noticeable and they hadn't gotten in to the really wild mechanics of the later expansions.
Solemn Wishes doesn't have a mana cost, so it can't be cast. Cards without costs aren't free in Magic, they're actually uncastable by normal means.
LP isn't health in Magic. It's called Life. So yeah, you'd gain 500 LP, which would be some kind of spendable currency like energy, but you'd have nothing to spend it on, and it wouldn't do anything to your life total.