So basically…

This is a legendary minion that costs 3 more than Summoning Stone
(5 mana – 0/6 whenever you cast a spell, summon a minion of that same cost)
has 7 attack and +1 health.

Difference
-Medivh can attack without buffing it, gives you the option of using the weapon as a tool, or as a mini-summoning stone.

The staff is also a weapon, there are 3 cards that can deal with it as the opponent,
Acidic Swamp Ooze, Harrison Jones, and Bloodsail Corsair (1-mana 1/2 remove 1 durability from the opponent’s weapon. Highly unplayed pirate card)

Bonus- This is the second way to gain a weapon as any class (Blingtron 3000 being the first), you can buff it with other neutral cards. However I expect this to be played mostly in Yogg decks (because it’s a big minion, gives you the option to utilize a weapon, and gives you minions for playing spells… duh)

Most likely this WONT be played as a regular weapon because it’s only 1 attack on it’s on, and the soonest it can be played is turn 3 as druid who’s going second. (Turn 3- 3 mana +5 (Double innervate and coin) giving you a turn 4 possibility to have a 7/7, a swipe to hit his minions, and a 4 cost minion.

Most likely will be played in decks where there are good minions at good spell cost slots, or flood the board.

Just food for thought

Here’s the thing about Discard-lock with the current revealed cards.

5 cards that discard in Warlock and Deathwing.

Benefits from discarding
Fist of Jaraxus- deal 4 damage to random enemy character when discarded
Tiny Knight of Evil- 3/2 2 cost minion, gain +1/+1 whenever a card is discarded.
Malchezzar’s imp- Draw a card whenever you discard a card.
and now this- Summon when discarded.

Great, but the benefits are really, really lack-luster because if you are playing discard, you run the risk of discarding the wrong card.

Say this-
Turn two, your hand is Succubus (2 mana 4/3 BATTLECRY: discard a random card) this card, and Doomguard.
Your opponent has a minion out and you can’t afford to not play it, lest risk being behind.

And as we know, if you pass a turn doing nothing, unless you have a board clear soon, you won’t survive.

So you play Succubus- problem?
There are a lot of 3/2 minions, and if you lose Doomguard, you just lost a ton of Tempo for turn 5.

Even if you have Malchezaar’s imp out beforehand, great… but if you don’t have an amazing turn around, having a 4/3 and 3/3, over having a 4/3 and losing Doomguard (Or any other card you want for that matter) odd’s you make this viable? Pretty slim

Alternative- Be able to choose what’s discarded. To me that’s the only way discardlock will ever be a thing, there is too much RNG in this deck type where you’re either really lucky, but then have to deal with being behind in hand from discard, or being ahead in fatigue if you had Malchezaar’s imp out.

Also think of it this way- if you want to discard some cards you’d need like 10 cards you want discarded, what are the odds you discard that over your entire hand?