Hearthpwn

I think folks are confusing "bad" with "unexciting" (or even "boring"), which this card definitely is, but in no way this is bad. It's 3 mana that gives you a spell you want OR gives your opponent one that they don't WHILE denying their next draw and giving you a spider tank, which means no drawback on stats for the cost. Good but boring. Boring but good.

Its Discover Any spell
not mage spell only
makes it more interesting

that is never how discover has worked. you always discover a class spell

It is "Discover Any Spell" if it explicitly says that like "Discover a spell from any class." 
see this Discovery of Magic

Then that card does not make sense yeah
though what confused me about it cuz i did see some cards explicitly say mage cards

also we ave Haataru, so then this card is quite confusing cuz haataru is just simply better
there are not really much self destructive or bad mage spells indeed to give to the opponent. its going to be always valuable

Underwhelming, but I think people are underrating it a bit. You could potentially waste an opponents draw by giving them a card that is unplayable for them, such as Divination. Not really a card you build your deck around, but maybe could fit into some deck.

Absolutly underwhelming.

I can discover a Mage spell with 1/3 of Mage cards, and the only advantage if that if I wiff I can potentially delay one draw from my opponent. And that's it? Even if was good, which it isn't, dosn't has enough appealing to run in a deck. I literally rather run Merch Seller (which is pretty bad) or even Vulpera Scoundrel so If I wiff I have a 4 option.

What's the best scenario with this? I put Supernova on turn 3 on top of my opponent's deck, to then give them a lot of value for free on the late game. Or I play this and I discover a spell which, I could do with any other card. I don't know. Is quite a wherever card.

this is a great card. It's at least a 4/5 star card. Guys, this is a 3 mana 3 4 with discover a spell. If you wiff and all 3 options are bad, then you pick the worst one and give it to the opponent and deny them a card draw or worse: you could give a control deck with 9 cards in hand draw, Pocket Dimension or Supernova which will essentially eat a hand slot for the rest of the game and cause them to make inefficient plays to avoid overdrawing. Imo this will probably be a safe auto-include for the entire year unless there's a deck that specifically wants you to not include it i.e. minionless mage

"this will probably be a safe auto-include" 

This is exactly why this card is one of the best. The majority of the big beasts in the set need to build your entire deck around them but this does not. The effect is powerful enough too.

"... If it's played, repeat this at the start of your next turn." At a higher mana cost or some condition of course. With it only being a one time thing it feels rather lame as a Legendary. At least the effect is unique and interesting. Unlike the other Mage Legendary.

This is so bad.  At least make it say something like "Discover a spell, it costs 1 less. Or give it to your opponent and it costs 1 more."

  At a minimum.. 

I'm gonna get this on the track aren't I?

I think it was nerfed during the design phase. 

Yeah. Could potentially see this being more powerful if you discovered a spell and put the other two options on top of the opponents deck. That is my guess as to what it was before.

should be "Discover a spell. put it on top of your opponent's deck and keep the other."

I could see a situation where your opponent is top decking with no cards in hand, and you could potentially put something useless on your hand to prevent them from drawing a card they need to win.

But that is so situational.  Not sure this is legendary worthy!

Battlecry become a spider tank or discover a spell.
This feels like a common that would support their dark gift mechanic

This needs to be buffed to (2) mana already. Even then it’s average as hell.
taking up the mantle of worst legendary of the expansion, with other past recipients such as the trash Rogue legendary from GDB that gives you a Backstab.

And warlock gets a fucking pig that gives you a card costing OPPONENTS life? Mage gets THIS? Never have I been Salty but this is some next level shitbending, they want to put mage down underground. How many favors did Warlock use to get a potential WINDFURY CHARGE 10 DAMAGE FUCKING TREE And mage gets a 3 mana drop GIVE YOUR OPPONENT A CARD

Boring card, I mean techniclly you could use it to delay your opponent if they are digging for resources but feels like most of the time you will just take your best option and a 3/4 that discovers a spell isn't that special it might see play for sure but it feels pretty average.