Very old/rare, and bonkers powerful.

The whole game is about what you do with mana (currency).
If all we are looking at is the mana, this lets you pay for other cards on your first turn that you normally wouldn't be able to play until the 4th turn of the game. That's a huge advantage.

/u/DerisionConsulting@lemmy.ca is right on the money. Mana paces the game, so anything that can break that is super good. In an otherwise even matchup, if one player has a Lotus while the other doesn't, that can easily make the game. It's not going to win the game in and of itself, but it's a huge enabler to play the thing that will win you the game, before your opponent can reasonably do anything about it.

On top of that, it's literally good in all decks. It's been banned in every format besides Vintage, where it's restricted to one (and not including casual/fan formats). It had to be banned partly for power reasons, but also because it makes deck-building less diverse. There's no deck that wouldn't want a Lotus if it could have one, much less four.

It's also part of the Reserved List. After WotC overprinted cards, they essentially promised not to reprint certain ones. I think it's a dumb decision, but they've annoyingly stuck to it (and players are worse off for it). Black Lotus is on that list. And it was alreadly limited in printings, because it was a rare card, and a bit of a design mistake.

It's also simply an iconic card. Despite being a design mistake, it's a major part of Magic history, and gets referenced all the time. To some extent, it's famous for being famous. That makes it the biggest prize for collectors.

So, all this together, it has an incredibly high demand, a very limited supply, and no indication of a reprint anytime soon.

So I printed off a proxy at a professional card printer for 30¢. :)

not all that extremely powerful

It’s game-breakingly powerful. It lets you get 3 mana for free instantly. Combined with spells that let you draw extra cards, this can result in having unlimited resources to do whatever you want on the very first turn of a game.

This is often cited as the most powerful card ever printed.

Very few cards are strong enough that they form part of a first-turn-kill, with the vast majority of decks, it's not remotely possible to get enough mana to play the kinds of cards that would end the game before your opponent can even do anything. Black Lotus gives you three mana, without having to play a land. If you're trying to build a hyper-broken combination, it's much easier to do if you have a black lotus.

Even outside of hyper-broken combinations, black lotus contributes heavily towards mana ramp, a mechanic that a large number of decks rely on to get going.

MtG has a lot of extremely powerful cards, but most of those are still somewhat situational. Black Lotus is a card you could add to almost any deck and improve that deck. It's so universally broken that it's impossible to build a deck that can't be improved with a black lotus... unless that deck already has four black lotuses.

As for it's value... they printed 500 of them. Total. The cost you'd pay for a black lotus is "highest bid at auction" - they don't really have a list price, because it's determined entirely by "is there one for sale right now?"

https://www.youtube.com/watch?v=AAvLC3fz068